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The Recapitulation Theory 
 and Human Infancy 
 
 BY 
 
 PERCY E. DAVIDSON, Ph.D. 
 
 I: 
 ASSOCIATE PEOFESSOB OF EDUCATION, LELAND STANFORD JUNIOR UNIVEBSITT 
 
 TEACHERS COLLEGE, COLUMBIA UNIVERSITY 
 CONTRIBUTIONS TO EDUCATION, NO. 65 
 
 PUBLISHED BY 
 
 SJrarljrra (flnUrgr, Glalnmbta Itttttrrrettij 
 
 NEW YORK CITY 
 
 1914 
 
Copyright, 1914, By 
 Percy E. Davidson 
 
ACKNOWLEDGMENTS 
 
 This paper was presented to the Division of Philosophy of 
 Columbia University as a doctoral dissertation. It was written 
 under the direction of Professor John Angus MacVannel, of 
 Teachers College, to whom is made grateful acknowledgment 
 of kind encouragement and valued suggestions. The writer 
 welcomes the opportunity of expressing his sense of an indebt- 
 edness of a fundamental character to the teachings and gen- 
 erosity of Professor John Dewey. Thanks are due also to 
 Professor J. Perrin Smith, of the Department of Geology in 
 Stanford Unversity, for his courtesy in reading the manuscript. 
 
 P. E. D. 
 
CONTENTS 
 
 CHAPTER I P AQB 
 
 Introduction 1 
 
 CHAPTER II 
 
 The Recapitulation Theory in Bioloqt: A Sketch of its History 
 
 Sec. 1. Other Names for the Theory 5 
 
 " 2. Anticipations of the Recapitulation Idea 5 
 
 " 3. The "Theory of Types" 7 
 
 -^" 4. Von Baer's Law: The Law of Embryonic Resemblance 8 
 
 " 5. The Correspondence Stated as Between Developmental Stages 
 of Existing Animals and the Succession of Adult Forms of 
 
 Extinct Representatives. Agassiz 9 
 
 6. Embryology and Darwinism 11 
 
 " 7. Darwin 11 
 
 " 8. The Developmental-ancestral Correspondence Clearly Enunci- 
 ated: Fritz Muller 14 
 
 — >f' 9. " Ontogeny is a Short and Rapid Recapitulation of Phylogeny": 
 
 Haeckel 14 
 
 " 10. Herbert Spencer 20 
 
 " 11. The Laws of Acceleration and Retardation 23 
 
 12. The Facts of Recapitulation 28 
 
 <^a. Those of Palaeontology 29 
 
 ~*3>. Those of Embryonic Resemblance 33 
 
 — ■ a 9c. Those of Comparative Morphology 37 
 
 ^5" 13. Recapitulation and the Physiology of Development 41 
 
 ^" 14. Biological Opinion Regarding Recapitulation 49 
 
 " 15. Review and Summary 57 
 
 CHAPTER III 
 
 Human Infancy and Recapitulation 
 
 Sec. (^l) Human Embryogeny 62 
 
 " 2. The Theory of Infancy 64 
 
 " 3. Recapitulation and Human Infancy 77 
 
 " 4. Cultural Recapitulation 93 
 
 t Conclusion , 
 
 CHAPTER IV 
 99 
 
 v 
 
THE RECAPITULATION THEORY 
 AND HUMAN INFANCY 
 
 CHAPTER I 
 
 INTRODUCTION 
 
 The strong interest in its biological and anthropological set- 
 ting which attended the beginnings of the systematic study 
 of childhood in this country has somewhat abated. Among 
 other things practical considerations have drawn attention 
 away to urgent matters of institutional management, while 
 newer and more exact methods, borrowed from the nearby 
 sciences, have been enthusiastically resorted to in the hope 
 of a more immediately serviceable knowledge of childhood 
 than any search into its history could reasonably be expected 
 to yield. 
 
 Doubtless this change of emphasis is a wholesome one. Ed- 
 ucation has still to find its most advantageous methods, if 
 indeed it has not yet to delimit its field. It is only right, then, 
 that all the methods which have done excellent work in the 
 sciences should be tested and evaluated for their usefulness 
 in its service. It would be a mistake, however, to regard this 
 departure from biology and anthropology as a final one, and 
 to conclude that education has nothing to learn from these 
 sources. Man's animal heritage is too intimate a part of him, 
 and his historical career too significant of his make-up, ever 
 to justify a neglect of these things on the part of those who 
 propose to mould his present condition and in some measure 
 to direct his future. 
 
 It may be, too, that some sense of disappointment has figured 
 in this willingness of students of childhood to turn in new 
 directions. Fruitful as it was in suggestion, the older genetic 
 line of approach could not, in the nature of the case, lead to 
 
 1 
 
2 The Recapitulation Theory and Human Infancy 
 
 a scientific basis for a practical educational program. This 
 could come only with the aid of an exact and faithful inter- 
 pretation of childhood as it exists in modern societies. Ed- 
 ucational schemes based upon historical inferences were there- 
 fore necessarily precarious and could easily be found unsound 
 when fairly tested. More especially has the older genetic 
 method of study suffered from the discredit into which some 
 of its guiding principles have fallen. One of these principles 
 was embodied in the theory of recapitulation, the idea that the 
 child in its development rehearses the history of its ancestry, 
 and that in consequence its nature may be inferred from the 
 probable course of human evolution. Taken bodily from em- 
 bryology, this idea was projected upon the field of mental gen- 
 esis, where it became a commonplace. More recently dis- 
 quieting rumors from the source of its origin have been heard 
 to the effect that the principle was formulated without suffi- 
 cient warrant, and that it cannot be depended upon even as a 
 helpful hypothesis. Its prestige has in consequence been ser- 
 iously damaged and there is plainly evident great uncertainty 
 as to the degree of truth it may contain. 
 
 This uncertainty with regard to a principle with important 
 implications for the theory of infancy and psychogenesis, is 
 hardly excusable or necessary. For recourse to the science 
 from which the principle was derived is open, and no obvious 
 reason exists why its real standing there should not be known. 
 If education is to be spared the humiliation which comes in- 
 evitably from building on the sand, it must earnestly endeavor 
 solidly to ground its doctrine. Especially is this true when 
 this doctrine is drawn from the pure sciences, for a thorough 
 knowledge of these on the part of outsiders is not easy of attain- 
 ment and a little knowledge is a dangerous thing. Moreover, 
 the position of education is peculiarly difficult, for as an art 
 its practice is not only dependent upon science as such; more 
 than one science is implicated. Education is none the less 
 in duty bound either to acquaint itself with the true value of 
 these borrowed principles or to leave them alone. 
 
 This paper represents an effort to discover something of the 
 status of recapitulation in biology and to note its implications 
 for the period of infancy. It makes no pretensions to scholarly 
 exhaustiveness. Its justification is the lack of any accessible 
 
Introduction 3 
 
 account of the history and present position of the idea to which 
 students of psychogenesis may refer, and its one merit is that 
 it stands for a conscientious attempt to understand and report 
 some of the more obvious aspects of the discussion. At some 
 future time someone with the requisite knowledge of biology, 
 anthropology, and psychology will do full justice to the topic 
 and supply us with an authoritative account of the matter. 
 Meanwhile we can at least clear away the superficial obstacles 
 and prepare ourselves for the more complete statement. 
 
 No one can justly object to a desire on the part of students 
 of childhood to know its biological history and its nature in con- 
 sequence. It is at least a legitimate object of curiosity. More 
 than this, no situation ever failed to become more intelligible, 
 and so more amenable, in the perspective yielded by its history. 
 On the side of possible cultural homologies in infancy and child- 
 hood there is the chance of a more direct usefulness. Some 
 years ago Professor Dewey inquired pointedly as to what good 
 could come from a knowledge of the historical genetic order, 
 when an argument from it directly to the proper treatment of 
 growth is not warranted. And it must be admitted that there 
 are positive limits to the use of principles derived from this 
 source. Education must be based primarily upon a knowledge 
 of the ontogenetic order itself. But it appears already that the 
 ontogenetic order is not easy of discovery. Although childish 
 and youthful performances can be objectively described and 
 in many cases measured, the true inward significance of 
 these performances is determined with the greatest diffi- 
 culty, because it is ultimately a matter of interpretation. Is 
 it not possible, then, that a knowledge of historical processes 
 may have something to offer, not as principles upon which ac- 
 tion shall be based, but as cues and hypotheses with which to 
 approach the exceedingly intricate phenomena of individual 
 psychogenesis? Historical processes expressed themselves slow- 
 ly. They were made with difficulty and became registered 
 step by step in objective products which lie open the world 
 over for sympathetic inspection. If a warrant can be found in 
 general terms for some degree of correspondence between in- 
 dividual psychogenesis and social or historical development, 
 it seems not impossible that a close study of the latter order 
 may yield suggestions of real value with which to approach 
 
4 The Recapitulation Theory and Human Infancy 
 
 the difficulties of the first. At least the possibility should not 
 be denied in advance of a fair trial. Obviously the resources 
 of child psychology would be immensely amplified if they might 
 include those of comparative psychology and ethnology. This 
 hope may stand as some justification for the present effort 
 to clear away some part of the obscurity which gathers about 
 the relations of the child and the race. If this should be in- 
 sufficient there still remains the interest which attaches to a 
 knowledge of the net result of one phase of a significant pioneer 
 movement in the study of childhood. 
 
CHAPTER II 
 
 THE RECAPITULATION THEORY IN BIOLOGY: A 
 SKETCH OF ITS HISTORY 
 
 1. Other Names for the Theory. 
 
 "This has been named by Hatschek the 'morphogenetie 
 theory,' by Hyatt the 'law of morphogenesis,' by Haeckel the 
 'biogenetic law,' by Cope the 'doctrine of parallelism,' and by 
 Morgan the 'repetition theory.' Sometimes it has been alluded 
 to as the 'law of von Baer,' but incorrectly, for von Baer was 
 its severest critic." 1 
 
 2. Anticipations of the Recapitulation Idea. 
 
 The idea that embryos of higher forms pass through the 
 adult stages of the lower animals is a very old one and no one 
 name is associated with its origin. The first clear reference 
 to it appeared at the end of the eighteenth and the beginning 
 of the nineteenth centuries. The system of classification then 
 in vogue was that of Linnaeus, which placed the various groups 
 one above the other in a single scale or series from the lowest 
 to the highest. In this scale the worms held the lowest rank, 
 and then in order, the insects, fishes, amphibia, birds, mammals. 
 The allusions to the animal series in the extracts which follow 
 are therefore to this uniserial system. 
 
 In these early expressions embryonic or developmental 
 stages were naturally found to resemble the mature forms of 
 existing lower animals, evolution as yet being a conception 
 of a very few prophetic minds. One of the earliest of these 
 expressions, however, was that of such a prophetic mind. Lor- 
 enzo Oken, a speculative evolutionist and a popularizer of the 
 science of the time, wrote in 1805, 
 
 "Each animal 'metamorphoses itself' through all animal 
 forms. The frog appears first under the form of a mollusk in 
 order to pass from this stage to a higher one. The tadpole 
 
 1 Montgomery, Analysis of Racial Descent In Animals, 1906, p. 177. 
 
 5 
 
6 The Recapitulation Theory and Human Infancy 
 
 stage is a true snail; it has gills which hang free at the sides of 
 the body as is the case in Unio pictorum. It has even a byssus, 
 as in Mytilus, in order to cling to the grass. The tail is nothing 
 else than the foot of the snail. The metamorphosis of an insect 
 is a repetition of the whole class, scolopendra, oniscus, julus, 
 spider, crab." 2 
 
 Later, in 1883, Oken wrote, in reference to the same matter, 
 
 "There is no doubt that we have here a striking resemblance, 
 and one that justifies us in thinking that the development in 
 the ovum is merely a repetition of the story of the creation of 
 the animal groups." 3 
 
 Here, plainly enough, is a statement in crude form of the idea 
 of recapitulation which was to have clear definition with the 
 advent of the doctrine of descent, and which was destined to 
 play so important a role in the history of that doctrine. 
 
 The other early references to be noted make comparisons 
 of development with the rank of existing animals. Thus, Wal- 
 ther, in 1808, said, 
 
 "The human foetus passes through its metamorphosis in the 
 cavity of the uterus in such a way that it repeats all classes of 
 animals, but, remaining permanently in none, develops more 
 and more into the innate human form. First the embryo has 
 the form of a worm. It reaches the insect stage just before its 
 metamorphosis. The origin of the liver, the appearance of the 
 different secretions, etc., show clearly an advance from the 
 class of the worm into that of the mollusk." 4 
 
 The embryologist Meckel, in 1808, 1811, and 1821, gave 
 greater definiteness to these comparisons: 
 
 "He held that the embryo of higher forms, before reaching 
 its complete development, passes through many stages that 
 correspond to those at which the lower animals appeared to be 
 checked through their whole life. In fact the embryos of higher 
 animals, the mammals, and especially man, correspond in the 
 form of their organs, in their number, position, and proportionate 
 size, to those of the animals standing below them. The skin is 
 at first, and for a considerable period of embryonic life, soft, 
 smooth, hairless, as in the zoophytes, medusae, many worms, 
 mollusks, fishes, and even in the lower amphibians." 6 
 
 » Quoted by Morgan, Evolution and Adaptation, 1903, p. 59. 
 ' Quoted by Bolsche, Haeckel, His Life and Works, translated by J. McOabe, p. 
 227. 
 
 'Quoted by Morgan, loc. cit., p. 59. 
 
 nwa. 
 
The Recapitulation Theory in Biology 7 
 
 Many other instances were given by Meckel, some fantastic 
 and absurd, others still to be found in the text-books on em- 
 bryology. It was this conception that met with the opposition 
 of von Baer, writing in 1828. Von Baer refers to 
 
 "The accepted idea, that the embryo in higher .animals passes 
 through the permanent forms of the lower. . . . This idea, 
 which was born in a time when, besides Malpighi and Wolff, 
 no connected investigations had been undertaken upon the 
 early periods of the embryology of any animal, and was especi- 
 ally carried out by a man who possessed perhaps the most 
 knowledge upon the embryology of the higher organisms, could 
 not help but arouse great support, because it was based upon a 
 multitude of special proofs. . . . Some supporters were so 
 zealous that they spoke no longer of similarity, but of complete 
 identity, and acted as though the correspondence were proven 
 universally and in each particular. We read a short time ago, 
 in a paper upon the blood circulation of the embryo, that the 
 human embryo does not omit a single animal form." 6 
 
 "That," remarks Montgomery, "must indeed have been the 
 luscious Springtime of the theory!" 
 
 Von Baer urged against the prevailing view of recapitulation 
 
 " (1) that no adult animal ever has a yolk sac, or (2) is sur- 
 rounded by embryonic fluids; (3) that it is not the case that an 
 embryo of a higher animal in each embryonic stage corresponds 
 in every point with an adult of a lower species, or (4) that in 
 the ontogeny of a lower form structural relations do not occur 
 which are found in the adult of a higher; (5) that it is equally 
 not the case that parts which are characteristic of only the high- 
 est forms appear latest in the ontogeny." 7 
 
 8. The " Theory of Types." 
 
 Recapitulation in its next phase became intimately involved 
 in that scientific theory of the natural world which preceded 
 the evolutionary or Darwinian conception now current, and 
 which stubbornly contested the claims of the latter until over- 
 whelmed by an incontrovertible array of fact. It is known as 
 the "theory of types," and is associated especially with the 
 names of Georges Cuvier, Louis Agassiz, Johannes Mueller, 
 and Richard Owen. The conception has been analyzed and 
 traced to various sources by Merz in his "History of European 
 
 • Quoted by Montgomery, loc. cit., p. 177. 
 1 1bid. p. 176. 
 
8 The Recapitulation Theory and Human Infancy 
 
 Thought in the Nineteenth Century." 8 Only its more general 
 character need be noted here. It was, in brief, the logical culmi- 
 nation of the progress of descriptive science following the Re- 
 vival of Learning. From independent beginnings, embryology 
 and physiology, comparative anatomy, geology and geography, 
 and botany, had by degrees and in unrelated ways accumulated 
 a vast amount of unorganized knowledge which by the first 
 quarter of the nineteenth century invited a general and unified 
 formulation. The outcome was a conception constituted in 
 part of inductions and analogies derived from the observation 
 of nature, in part of the literal biblical interpretation of the 
 overshadowing Puritanism of the time. 9 
 
 In this theory the plan of arranging the animal groups in 
 a single scale or series gave way to a system in which the species 
 were regarded as modifications of four main "types" or "em- 
 branchements," independent and equivalent "plans of struc- 
 ture," namely, the vertebrate, articulate, radiate, and mol- 
 luscan. The species representing these great types were 
 "fixed," in the sense that they had been separately created 
 as they were found to be, and were in no wise genetically related. 
 The study of fossils and geological formations led to the addi- 
 tional idea that species had suffered extinction coincident with 
 colossal revolutions or catastrophes in the life of the planet, 
 succeeded by the creation of new types. Only by the intervention 
 of such episodes could be explained the succession of life forms 
 so unequivocally indicated in these phenomena. 
 
 4. Von Baer's Law: " The Law of Embryonic Resemblance." 
 
 Von Baer was identified with the theory of types; in fact he 
 seems to have had some share in its formulation, although he 
 did not go to the extremes of its chief exponents. His views of 
 the significance of embryonic development are therefore to be 
 understood with this theory as a background. For von Baer 
 did not merely criticize the prevailing ideas of Meckel and others 
 on this subject. A distinguished embryologist, he held original 
 and striking ideas of his own, which had a large place in the 
 subsequent history of the discussion. Von Baer's position is 
 represented by the following laws, which he formulated: 
 
 'Vol. II, Chap. IX. 
 
 » Poulton, Essays on Evolution, pp. 56, 57. 
 
The Recapitulation Theory in Biology 9 
 
 " (1) That the general of a large animal group expresses itself 
 earlier in the embryo than the special. (2) Out of the most 
 general of the structural relations evolves the less general, and 
 so forth until finally the most special appears. (3) Each em- 
 bryo of a particular animal form instead of passing through the 
 other particular forms, separates itself rather from them. (4) 
 In reality accordingly the embryo of a higher form is never like 
 to another animal form, but only to its embryo." 10 
 
 Morgan illustrates the se laws ji sjpjloras.: 
 
 " For example two similar species of pigeon s will follow the 
 P^/ pnp mpt,V|n^ of development up to almost theTa.StjgjgggXjf'their 
 formation , Thn em bryos ot t hese two forms will be_praclical^ 
 identical until each p roduces th e_speciar characters_of _its jo wn 
 s pgp i e^s . On tFe~other hand twoanimalsbelonging to different 
 ' Tamihes of the same phylum will have 6nly"tne^rlier~stages~ih 
 ^ojanaoBy- Thus,^^bird ancf'a: mam mai'will haveTBe nrst .stages 
 similar, or Identical, and then diverge, the mammal adding the 
 higher characters of its group. The resemblance is between 
 corresponding embryonic stages and not between the embryo 
 of the mammal and the adult form of a lower group. 
 
 "Von Baer was also careful to compare embryos of the same 
 
 phylum with each other, and states explicitly that there are no 
 
 grounds for comparison between embryos of different groups. ~n 
 
 f . . In one place von Baer raises the question whether the 1 
 
 I egg may not be a form common to all the phyla." 11 J 
 
 The phyla alluded to are, of course, the four great groups or 
 types. It is important to remember that von Baer had reference 
 in his statements to likenesses among existing animals, and not 
 to ancestral relationships. Von Baer did not accept evolution 
 although the issue between the two theories had been well 
 drawn before his death. Later Herbert Spencer pointed out 
 that a thoroughgoing application of von Baer's law in filial and 
 ancestral relationships implied the recapitulation of Oken, that 
 is, the idea that the embryogeny "repeated the story of the 
 creation of the animal groups." 
 
 6. The Correspondence Stated as between Developmental Stages of 
 Existing Animals and the Succession of Adult Forms of Extinct 
 Representatives. Agassiz. 
 
 Von Baer's significant contribution to the discussion did not 
 exert an immediate influence. It was Louis Agassiz, a pupil of 
 Cuvier, the principal originator of the type theory, who made 
 
 « Quoted by Montgomery, loc. cil., p. 178. 
 "Loc. cit., p. 61. 
 
10 The Recapitulation Theory and Human Infancy 
 
 recapitulation an integral element in this theory and gave it its 
 new form. Early in his life Agassiz entered upon elaborate 
 studies of living and fossil fishes and so came upon resemblances 
 between developmental phases of living animals and the adult 
 forms of their extinct representatives. As his interest broadened 
 to include the systematic classification of the whole animal 
 world, Agassiz relied more and more upon the facts of embry- 
 ology to make good the deficiencies of fossil remains and to pre- 
 vent the confusion, inevitable as he believed, from an examina- 
 tion of anatomical differences alone. In 1857 he wrote, "I satis- 
 |fied myself long ago that embryology furnishes the most trust- 
 fworthy standard to determine the relative rank among animals." 
 In the system ultimately evolved by Agassiz, descriptive of 
 what he believed to be the natural order, there were four great 
 parallelisms, or systems of relationship. These were (1) a paral- 
 lelism between the geological succession of animals and their 
 relative standing or structural gradation; (2) a parallelism be- 
 tween the geological succession of animals and the individual 
 development of their living representatives; (3) a parallelism 
 between the relative rank or gradation of animals and their 
 individual development; and (4) these several series were again 
 related to geographical distribution. Thus 
 
 "the phenomena of animal life correspond to one another, 
 whether we compare their rank as determined by structural 
 complication with the phases of their growth, or with their suc- 
 cession in past geological ages; whether we compare this succes- 
 sion with their embryonic growth, or all these different relations 
 with each other and with the geographical distribution of ani- 
 mals upon earth. The same series everywhere!" 12 
 
 This interlocking system of relationship constituted the ground- 
 work of the "plan of creation" Agassiz's "Essay on Classifica- 
 tion " was meant to delineate, a plan very satisfying to his own 
 religious sentiments, if indeed it was not inspired by them. 
 "Shall we," he exclaims, "by any false argumentation, allow 
 ourselves to deny the intervention of a Supreme Intellect in 
 calling into existence combinations in nature by the side of 
 which all human conceptions are child's play?" 13 
 
 "Essay on Classification, 1857, p. 196. 
 "Ibid., p. 197. 
 
The Recapitulation Theory in Biology 11 
 
 It was the second parallelism, that between the succession in 
 geological time and the embryonic stages of living representa- 
 tives, that constituted the new phase in the history of recapitula- 
 tion. Of this he said more particularly, 
 
 "These relations, now they are satisfactorily known, may also 
 be considered as exemplifying, as it were, in the diversity of 
 animals of an earlier period, the pattern upon which the phases 
 of the development of other animals of a later period were to be 
 established. They appear now, like a prophecy in those earlier 
 times, of an order of things not possible with the earlier combina- 
 tions then prevailing in the animal kingdom, but exhibiting in a 
 later period, in a striking manner, the antecedent considerations 
 of every step in the gradation of animals." 14 
 
 There is here suggested Agassiz's well known concept of 
 "prophetic types," the facts for which, as well as for his "syn- 
 thetic" and "progressive" types, were so significant to other 
 minds of a genetic relationship he himself refused to acknowledge. 
 
 6. Embryology and Darwinism. 
 
 This correspondence between embryonic stages and the geo- 
 logical succession of animal forms was destined to play an im- 
 portant part with the advent of Darwinism (" Origin of Species," 
 1859). It will be well to indicate at once the three allied uses 
 to which the facts of embryology were put in the development 
 of this theory. They became, in the first place, one main sup- 
 port to the doctrine of descent itself. This was naturally the 
 value attached to them chiefly by Darwin. Once the doctrine 
 was accepted, embryology was employed with all degrees of 
 assurance to determine the affinities of living animals in the 
 interests of a classification based upon genetic relationship. 
 Fritz M filler was one of the first of a long line of students to 
 demonstrate their usefulness from this viewpoint. Finally, as 
 this classification became elaborated, it made possible the trac- 
 ing back of genealogies, phylogenies, or racial histories, and this 
 was introduced systematically by Haeckel. 
 
 7. Darwin. 
 
 By the time of the sixth edition of the "Origin of Species'' in 
 1872, the two applications of the facts of embryology just men- 
 tioned had been made and had received the sympathetic notice 
 
 " Essay on Classification, 1857, p. 156. 
 
12 The Recapitulation Theory and Human Infancy 
 
 of Darwin. The contribution of Fritz Miiller to the classifica- 
 tion of the Crustacea, largely by the aid of embryology, had 
 been of particular interest to him, and Haeckel's work with 
 phylogenies was alluded to with approval. 15 
 
 Darwin's treatment of the facts under discussion is found in 
 Chapter XIV of the sixth edition where he deals with the mutual 
 affinities of organic beings. Referring to the efforts of the 
 "special creationists" to arrange a "natural system" in ac- 
 cordance with the divine plan, he urges that such a plan is mean- 
 ingless unless it relates to time and place and has a specific con- 
 tent, and that all the rules, aids, and difficulties in the then 
 current efforts at classification are well explained by a view of 
 a natural system founded on descent with modification. In 
 support of this contention he proceeds to submit to scrutiny the 
 several kinds of recognized affinities among animals, those of 
 embryology among them. After a citation of facts, including 
 some of von Baer and a direct reference to his law of embryonic 
 resemblance, Darwin asks, 
 
 "How then can we explain these several facts in embryology, 
 — namely, the very general, though not universal, difference in 
 structure between the embryo and the adult; — the various parts 
 in the same individual embryo, which ultimately become very 
 unlike and serve for diverse purposes, being at an early period 
 of growth alike; — the common, but not invariable, resemblance 
 between the embryos or larvae of the most distinct species in the 
 same class; — the embryo often retaining whilst within the egg 
 or womb, structures which are of no service to it, either at that 
 or at a later period of life; on the other hand larvae, which have- 
 to provide for their own wants, being perfectly adapted to the 
 surrounding conditions; — and lastly the fact of certain larvae 
 standing higher in the scale of organization than the mature 
 animal into which they are developed?" 
 
 The explanation is contained in the two principles, viz., 
 " . . . that slight variations generally appear at a not very 
 early period of life and are inherited at a corresponding not 
 early period." Darwin's illustration helps to make his meaning 
 plain, 
 
 "Now let us apply these two principles to species in a state 
 of nature. Let us take a group of birds, descended from some 
 ancient form and modified through natural selection for differ- 
 
 » Origin of Species, American ed., p. 231. 
 
The Recapitulation Theory in Biology 13 
 
 ent habits. Then, from the many slight successive variations 
 having supervened in the several species at a not early age, and 
 having been inherited at a corresponding age, the young will 
 have been but little modified, and they will still resemble each 
 other much more closely than do the adults, — just as we have 
 seen with the breeds of pigeons." 16 
 
 For Darwin did not fail to verify his statements by carefully 
 measuring young and old dogs, horses, and pigeons. Accord- 
 ingly, 
 
 "It is highly probable that with many animals the embryonic 
 or larval stages show us, more or less completely, the condition 
 of the progenitor of the whole group in its adult state." 
 
 Furthermore, "we can see why ancient and extinct forms so 
 often resemble in their adult state the embryos of existing species 
 of the same class. Agassiz believes this to be a universal law of 
 nature; and we may hope hereafter to see the law proved true. 
 It can, however, be proved true only in those cases in which 
 the ancient state of the progenitor of the group has not been 
 wholly obliterated, either by successive variations having super- 
 vened at a very early period of growth, or by such variations 
 having been inherited at an earlier stage than that at which 
 they first appeared. It should also be borne in mind that the 
 law may be true, but yet, owing to the geological record not 
 extending far enough back in time, may remain for a long period, 
 or forever, incapable of demonstration. The law will not strictly 
 hold good in those cases in which an ancient form became adapted 
 in its larval state to some special line of life, and transmitted the 
 same larval state to a whole group of descendants; for such 
 larvae will not resemble any still more ancient form in its adult 
 state." 17 
 
 These passages have a peculiar interest in the light of the 
 later history of the discussion. There is every intention evident 
 of doing full justice to the complexity of the facts and a plain 
 acknowledgment of a variety of cases. Nevertheless, one de- 
 tects an unmistakable leaning in the direction of a general state- 
 ment favorable to recapitulation, and in the allusion to Agassiz 
 an expressed sympathy for a "universal law of nature." With 
 the great authority of Darwin offering this much justification, 
 one cannot be surprised if in the hands of less careful students 
 the facts should be found to warrant a much more sweeping 
 statement. 
 
 i* Origion of Species, American ed„ pp. 245, 247, 249. 
 "Ibid., pp. 252, 254. 
 
14 The Recapitulation Theory and Human Infancy 
 
 8. The Developmental-Ancestral Correspondence Clearly Enunciated: 
 
 Fritz Miiller. 
 
 It has been noted that Darwin had profited by the contribu- 
 tion to his theory made by Miiller in his book, "Fur Darwin," 
 published in 1864. Torn between the claims of the rival theories, 
 Miiller determined rigidly to apply the principles of Darwin to 
 one group, the Crustacea, in order to discover whether lines of 
 descent and a genetic classification could in this manner be 
 determined within it. In concluding his study Miiller general- 
 ized upon the facts of resemblance between the developmental 
 history of descendants and the adult state of ancestors in a more 
 precise manner than Darwin had in his first edition. His con- 
 clusions are as follows: 
 
 "Descendants, therefore, reach a new goal, either by deviat- 
 ing sooner or later whilst still on the way towards the form of 
 their parents, or by passing along this course without deviation, 
 but then, instead of standing still, advance still further. 
 
 "In the second case the entire development of the progenitors 
 is also passed through by the descendants, and, therefore, so far 
 as the production of a species depends upon this second mode of 
 progress, the historical development of the species will be mir- 
 rored in its developmental history. 
 
 "The historical record preserved in developmental history is 
 gradually effaced as the development strikes into a constantly 
 straighter course from the egg to the perfect animal, and it is 
 frequently sophisticated by the struggle for existence which the 
 free-living larvae have to undergo. 
 
 "Which of the different modes of development at present 
 occurring in a class of animals may claim to be that approach- 
 ing most nearly to the original one, is easy to judge from the 
 above statements." 18 
 
 9. "Ontogeny is a Short and Rapid Recapitulation of Phylogeny:" 
 
 Haeckel. • 
 
 In the statement of principles quoted above from Fritz Miiller 
 it will be observed that there is no disposition to weight the cases 
 of recapitulation in very great disproportion to those of embry- 
 onic or larval deviation. Two possible courses of development 
 are shown, recapitulation being the second. And there is little 
 disposition, if any, to make the second class of cases the more 
 prevalent or the more characteristic in any fundamental way 
 
 18 Facts and Arguments for Darwin, pp. Ill, 112, 114. 
 
The Recapitulation Theory in Biology 15 
 
 It was noticed, too, that Darwin hesitated to formulate a gen- 
 eralization distinctly in favor of recapitulation, whatever may 
 have been his inclination. It remained for Haeckel to raise 
 M tiller's second class of cases into very great prominence at the 
 expense of the first, to assume that this represents the more 
 general, and indeed in some fashion a necessary order, and to 
 throw together all the cases of the first class as mere subsidiary 
 disturbances of the order represented by the second. Thus the 
 "law of recapitulation" took the form in which it is best known. 
 It is interesting to consider the consequences if by chance the 
 emphasis had been placed the other way round. Then the 
 "law" would have read somewhat as follows: Ontogeny records 
 the adaptations the life history of descendants has made in its 
 evolution and is indicative of its phylogeny in those cases only 
 in which embryonic or larval deviation has not occurred. 
 
 Haeckel's great popularity as a writer gave his statement 
 very wide currency, in fact, made it dominant. It has happened 
 in consequence that the whole succeeding history of the discus- 
 sion, including its application to mental growth, has turned 
 largely upon either the possible substantiation of his "biogenetic 
 law," or upon its possible refutation. It may be said with 
 justice that much of the mischief that has resulted from a care- 
 less use of his formula has been due to the particular form in 
 which the facts were thus summarized. 
 
 Haeckel- was a young man beginning his career at Jena when 
 Darwin's great book appeared. The circumstances of his train- 
 ing had been such as to prepare his mind for the new doctrine and 
 he became its most ardent advocate and disseminator in Ger- 
 many. Haeckel was not content to limit himself to a study of 
 the causes of descent. At once speculative and intrepid, he 
 carried the doctrine in every direction his system-loving mind 
 pointed, and ultimately built a complete natural philosophy 
 upon it. He would not demonstrate the kinships within one 
 class only, as had Fritz Miiller. Nothing less than a genealogical 
 tree of the entire animal world became his object. Haeckel was 
 particularly interested in the two extremes of descent concerning 
 which Darwin had been less explicit, that of the ancestry com- 
 mon to the great phyla among the lowest forms, and that of 
 man. His original investigations were consequently directed 
 upon the lowest orders and he was able to suggest a succession of 
 
16 The Recapitulation Theory and Human Infancy 
 
 steps by which the Metazoa had evolved from the simplest form 
 of living matter. This he in turn derived from the inanimate. 
 Haeckel was equally consistent in applying the doctrine of 
 descent to mankind. The groundwork of his entire system was 
 laid in the " Generelle Morphologie," published in 1866, his numer- 
 ous later publications being practically extensions of this work. 
 
 In this book Haeckel recurs to the threefold parallelism of 
 Agassiz between the order represented by the classification of 
 existing animals and those of palaeontology and of individual 
 development. 19 But in place of the mystic bond of connection 
 between the three of Agassiz, Haeckel substitutes a "close casual 
 nexus' ' derived from the theory of descent in the two factors of 
 heredity and adaptation. This primary conception assists in 
 the understanding of his attitude toward recapitulation, for it 
 is the keynote to his whole system. 
 
 When one considers the situation in 1866 and the nature of 
 his general purpose, it is not surprising that Haeckel should have 
 reverted to this threefold parallelism. To his mind Darwin 
 had shown conclusively the truth of the doctrine of descent with 
 modification. Obviously the hierarchy of living forms, from 
 the lowest one-cell condition through the several grades of 
 complication to the highest, was a result of descent, and was at 
 least suggestive of what the historical order had been. It 
 would therefore correspond with the actual historical order so 
 far as this was indicated by the succession of fossils in the earth's 
 formations. The gradual progression through development 
 from the ovum to the complicated adult was again suggestive 
 of this order in its broad outlines at least. All three of these 
 had served Darwin as foundations for his theory, and the least 
 plausible, that of development, had received a certain warrant 
 in fact in the writings of Darwin and Fritz Muller, besides 
 having had a respectable history prior to the descent theory. 
 Development, indeed, presented in the concrete the only avail- 
 able picture of what the idealized evolution of animals through 
 geological time presupposed. This suggestiveness of develop- 
 ment has often been alluded to since Haeckel, and still is, by 
 biological students. If one is content wtih exceedingly broad 
 
 " " . . .die Stufenleiter des nattirliclieii Systems mlt den parallen Stufenleitem. 
 der indlvlduellen und der palaontologischen Entwickelung in dem engsten mechani- 
 achen Causalnexus stent." Gen. Morph. II, XIX. 
 
The Recapitulation Theory in Biology 17 
 
 outlines one may still hold with justice for the truth of this 
 threefold parallelism. 20 Its recurrence with Haeckel was con- 
 sequently the obvious thing on the part of one who desired to 
 present a panoramic view of the natural world after the manner 
 of Humboldt and Agassiz. The imperfections of the parallel- 
 ism would naturally appear subsequent to its original formula- 
 tion. 
 
 It may have been the prestige of this parallelism in his mind, 
 together with the fact that he was for the time primarily a 
 morphologist, as the title of his book implies, that led Haeckel 
 to over-simplify the effects of heredity and adaptation through- 
 out descent, and to neglect somewhat the question of what was 
 required of these two factors to substantially support the paral- 
 lelism. This had been a matter of primary concern to Darwin 
 and Miiller, as has been noted. Throughout his works the 
 ontogenetic-phylogenetic parallelism is associated especially 
 with the "laws" of hereditary transmission at correspond- 
 ing ages and in corresponding place relations, and with that of 
 abbreviated heredity suggested by Miiller. 21 The effect of 
 the first two was to repeat the parental order; the effect of the 
 last was to simplify and shorten this order perhaps, but not to 
 destroy it. This is essentially the situation in the fifth edition 
 of the "Evolution of Man," 2 ' where the symbolic representation 
 of the two series indicates omission of ancestral stages, and some 
 modification of them in ontogeny without obscuring their 
 identity. 
 
 The appearance of novelty, or variation, was identified by 
 Haeckel with adaptation, or the direct modifying effect of 
 environment. This again would explain in part his over-em- 
 phasis of the conservative influence of heredity, for the ever- 
 recurring changes induced by germinal variations regardless 
 
 10 "It Is indisputable, if we only consider the most general features, that the history 
 of the development of an individual is a kind of rapid recapitulation of the slow phases 
 of the evolution of the species and of the branch." DepSret.Transformations of the 
 Animal World, trans. 1909, p. 254. 
 
 » " Der Parallelismus zwischen der phyletischen (palaontologischen) und dei bion- 
 tischen (individuellen) Entwickelung erklart sich einfach mechanisch aus den Verer- 
 bungs-Gesetzen und insbesondere aus den Gesetzen der gleichzeitlicben, der gleichart- 
 lichen und der abgektirtzen Vererbung. Alle Erscheinungen, welche die individuelle 
 Entwiekelung begleiten. erklaren sich lediglich, soweit sie nicht unmittlebares Eesultat 
 der Anpassung an neue Existenz-Bedingungen sind, aus der palaontologischen 
 Entwickelung der Vorfahren des Individuums. " Gen. Morph. II, p. 372. 
 
 » Trans., 1910, p. 4. 
 
18 The Recapitulation Theory and Human Infancy 
 
 of adaptation would be eliminated at one stroke. Adaptation 
 would effect embryonic and larval structures, as he clearly 
 points out, but presumably its principal effect would be to 
 extend the ontogeny in a linear way corresponding to a similar 
 linear extension of the phylogeny through geological time. 
 However this may be, one misses in the accounts of Haeckel 
 the detailed consideration of the effects of heredity, variation, 
 and adaptation in the life-histories of succeeding generations, 
 so noticeable in the treatment of Darwin and Miiller. This, 
 perhaps, is what reasonably might have happened from a pre- 
 occupation with the parallelism he presupposed. The upshot 
 of the matter is that Haeckel greatly overestimated the con- 
 serving force of heredity operating through descent. This 
 renders intelligible his concluding formula: "Phylogeny is the 
 mechanical cause of ontogeny," a true statement when the par- 
 ents and immediate ancestors are considered, only true with 
 respect to the remote ancestors in a phylogeny on the assump- 
 tion that the force of heredity has been fairly constant through- 
 out. 
 
 It would, however, be unfair to Haeckel to rest an inter- 
 pretation of his biogenetic law upon his formal summaries alone. 
 A consideration of the actual use to which the law was put 
 in elaborating phylogenies presents a somewhat different aspect. 
 For instance, in developing the phylogeny of man the argument 
 invariably proceeds from a comparison of embryonic resem- 
 blances to a discovery of the palingenetic, or racially older, fea- 
 tures by an elimination of the cenogenic, or more recent ad- 
 ditions. Once these older features are determined the bio- 
 genetic law is invoked and the ancestral reference made. In 
 the earlier stages the ancestral reference is to hypothetical 
 ancestral adult forms, as from the gastrula to the Gastraea, 
 or from the coelomula to the hypothetical Coelomaea, and a 
 sequence of such forms results, in keeping with recapitulation 
 in the ordinary sense of a chronological series. But in the 
 later and higher stages the ancestral reference is not to specific 
 ancestral adult characters, but to ancestors having an embry- 
 ogeny with similar features. This last may be illustrated 
 "We see," he says, "that man entirely resembles the higher 
 Mammals, and most of all the apes, in embryonic development 
 as well as in anatomic structure. And if we seek to understand 
 
The Recapitulation Theory in Biology 19 
 
 this ontogenetic agreement, in the light of the biogenetic law, 
 we find that it proves clearly and necessarily the descent of 
 man, from a series of other Mammals, and proximately from 
 the Primates." 23 From ontogenetic resemblances a common 
 ancestry is argued. Clearly this is not recapitulation in the 
 strict sense. But Haeckel is applying the biogenetic law as he 
 understands it, wherefore it must be that he means by recapit- 
 ulation in this application only that an ontogeny presents in 
 its racially older features evidence of value regarding its prox- 
 imate or less remote ancestors. Haeckel's formal general- 
 izations and their actual use thus do not appear wholly in 
 agreement, and if the meaning of principles lies more espec- 
 ially in the work they do, it must be admitted that the common 
 opinion of Haeckel's conception requires some modification. 
 It should be noted that the notion of recapitulation conveyed 
 by the practice just referred to brings Haeckel close to the 
 position of some of the most radical critics of his theory. 
 
 Whatever the case may be in these particulars, the general 
 effect of Haeckel's formal statements of the biogenetic law 
 was to imply a sequence in embryonic development such in gen- 
 eral that it was broadly descriptive of a similar sequence in 
 phylogeny. His qualifications of the law still did not have the 
 force of robbing the principal statement in the formula of 
 first-rate descriptive value. Moreover his language was such 
 as to suggest some fundamental tendency toward or necessity 
 for recapitulation, which might be obstructed partially so as 
 to "falsify" or "confuse" or "distort" this order. All this 
 is declared to be misleading in its implications. Ontogeny 
 is subject to many factors, of which those favoring recapitula- 
 tion are but of equal value, or even much less than equal value, 
 with the rest. And they are no more natural or to be expected 
 or primary than those with which they associate. 24 
 
 » Evolution of Man, trans., 1910, p. 307. 
 
 M Compare this statement from Miall: 
 
 "I diverge from him [Haeckel] when he says that each animal is compelled to 
 discover its parentage in its own development. ... I admit no sort of neces- 
 sity for the recapitulation of the events of the phylogeny in the development of the 
 individual. ... I am on my guard when he talks of laws, for the term is mis- 
 leading, and ascribes to what is a mere geneial statement of observed facts the force 
 of a command. The so-called laws of nature (a phrase to be avoided) may indeed 
 enable us to predict what will happen in a few cases, but only when the conditions 
 are uniform and simple — a thing which is common in Physics, but very raie in Biol- 
 
20 The Recapitulation Theory and Human Infancy 
 
 10. Herbert Spencer. 
 
 It is interesting to compare with the views of Haeckel the 
 position of another great systematist whose book appeared in 
 the same year with the "Generelle Morphologie." This book 
 is the "Principles of Biology" of Herbert Spencer. Spencer 
 makes his starting point von Baer's law and does not widely 
 depart from it throughout the account of his first edition. 
 He however cautions his reader against accepting the general- 
 ization as exact. The resemblances among related embryos 
 noted by von Baer "are not precise but approximate. Only 
 leading characteristics are the same : not all the details .... 
 each kind of organism, though having a general direction of 
 development like that of the others it is for a time traveling 
 with, shows from the first a tendency to leave the general route — 
 a tendency which presently becomes strongly marked." Still 
 as an average truth the generalization may be regarded as be- 
 yond question. But, "the generalization must not be con- 
 founded with an erroneous semblance of it that has obtained 
 considerable currency. An impression has been given by those 
 who have popularized the statements of embryologists, that 
 during development each higher organism passes through 
 stages in which it resembles the adult forms of lower organ- 
 isms. . . This is not the fact." Thus Spencer repudiates 
 recapitulation in the form it was taking with Haeckel. 25 
 
 In a later chapter where he presents with the others the 
 embryological arguments for evolution, Spencer is occupied 
 in showing that evolution explains not only the resemblances 
 of embryos but the lack of such resemblances as well. This 
 is due to the very unlike life conditions and consequent unlike 
 adaptations made by different groups in their evolution sub- 
 sequent to their departure from the common ancestor, adap- 
 
 ogy. " Eeport of the British Association for the Advancement of Science, 1897, p. 682. 
 Compare also the following from Hyatt : 
 
 "The use of terms indicating that Nature has confused or destioyed its own onto- 
 genetic records of the transmission of characters in certain cases assumes (1) that 
 these are exceptional cases, (2) that caenogenesis is not the normal mode of trans- 
 mission in certain types in which it occurs, (3) that both of these modes of trans- 
 mission are not affected by tachygenesis, all these implications being erroneous. 
 . . . "destruction," "confusion," or " f alsiflcation " are subjective terms inap- 
 plicable to the objective character of the phenomena . . . entirely out of place 
 in natural science." Phylogeny of an Acquired Characteristic, p. 401, footnote. 
 
 » Vol 1, 1st American ed., 1898, pp. 143, 144. 
 
The Recapitulation Theory in Biology 21 
 
 tations which are reflected in embryonic changes. As a result, 
 "the embryological parallelism is qualified by irregularities 
 that are mostly small, in many cases considerable, and occas- 
 ionally great." 26 
 
 The irregularities in the law noted by Spencer may be briefly 
 enumerated: (1) The substitution of organs and the suppression 
 of organs in certain embryos as compared with others, the 
 first illustrated by the succession of changes in the aerating 
 appliances of the mammalian embryo, the second by the 
 suppression of the foetal teeth of whales; (2) retrograde 
 development, as in the loss of limbs and senses in adult par- 
 asites; (3) substituted modes of development, the two typical 
 modes being direct and indirect. In the former case the 
 development of the animal proceeds from the egg to the adult 
 condition without intermediate stages. In the latter a cir- 
 cuitous route is to be noted involving often many metamor- 
 phoses. The latter mode is that of the higher or more com- 
 plicated animals because it reflects the many changes incident 
 to the embryo from the long succession of unlike conditions 
 through which the group has passed. The direct mode is there- 
 fore the substituted mode among the higher animals, the cause 
 being a prolonged constancy of conditions inducing finally an 
 adjustment of all parts of the animal to the settled condition 
 of its life as a whole. Similar facts are to be noted among 
 particular organs as such. 
 
 Subsequent to the publication of the first edition of the 
 "Principles of Biology" Spencer's views suffered a change of 
 emphasis. In later editions the condemnatory sentences re- 
 garding recapitulation are missing. He has found, in fact, 
 that von Baer's law, when carried out consistently in evolu- 
 tionary terms, implies recapitulation. 27 
 
 "This conception," says Spencer, "of a tree, symbolizing 
 the relationships of types and a species derived from the same 
 root, has a concomitant conception. The implication is that 
 each organism, setting out from the simple nucleated cell, must 
 in the course of its development follow the line of the trunk, 
 some main branch, some sub-branch, some sub-sub-branch, etc., 
 •of this embryological tree; and so on till it reaches the ultimate 
 
 « Vol. 1, 1st American ed., 1898, p. 368. 
 " See the first two laws of von Baer, p. 9. 
 
22 The Recapitulation Theory and Human Infancy 
 
 twig representing the species of which it is a member. It must 
 in a general way go through the particular line of forms which 
 preceded it in all past times: there must be what has been aptly 
 called a "recapitulation" of the successive ancestral structures. 
 This, at least, is the conclusion necessitated by the generaliza- 
 tion we are considering under its original crude form." 28 
 
 Thus in any unfolding embryo there are two sets of energies 
 at work, one tending toward the type of the primitive ances- 
 tors, the other toward the evolved terminal type, the inter- 
 mediate structures being influenced by their conflict. Still 
 other factors intervene to affect the character of development. 
 One is economy. A premium is placed upon any animal in a 
 series which can mature at a saving in vital energy. This tends, 
 to shorten the process. Economy again explains the entire 
 disappearance of intermediate forms in some cases. Economy 
 explains, once more, "preadaptation," in the earlier preparation 
 of structures and functions of increasing size and importance 
 in the life of the evolving animal. A demand for more time 
 in the upbuilding of increasingly complicated organs may also 
 bring about preadaptations. Finally the lack of uniformity 
 in the decrease and disappearance of organs may be explained 
 in several ways: large organs will suffer more than small ones 
 from the principle of economy; decrease in unused organs may 
 not coincide with the evolution of more important ones; ances- 
 tral features may become embodied as parts of new organs; 
 and some disused organs may entail evil by being in the way 
 of the modes of living. 23 
 
 Spencer's views are interesting in that while they arrive at 
 an acceptance of the chronological idea of recapitulation, they 
 do so by inferences directly from the law of von Baer. But 
 recapitulation is true only to the extent that von Baer's law 
 holds, and Spencer is very well aware of the variations from th& 
 law. His statements thus escape the extreme form given to 
 those of Haeckel by the latter's presupposition of a biogenetic 
 fundamental law. Spencer's position is representative of an 
 acceptance of recapitulation more just to the complexities of 
 the facts, and more nearly in accord with the views of Darwin 
 and Miiller. 
 
 »Loc. cit., p. 453. 
 "Ibid., p. 458, et seq. 
 
The Recapitulation Theory in Biology 23 
 
 11. The Laws of Acceleration and Retardation. 
 
 A notable series of investigations in which recapitulation 
 figured largely was inaugurated by Alpheus Hyatt in Boston 
 in the year 1866. Hyatt's original study was made upon fossil 
 shells of certain mollusks, but his method has been used by his 
 pupils and followers with various groups of mollusks and other 
 invertebrates, and even with the vertebrates. This school of 
 investigators has derived so much assistance from recapitulation 
 that they are now to be regarded as its chief defenders. In- 
 deed, one member of the school has declared that "If the em- 
 bryologists had not forestalled them, the paleontologists would 
 have had to invent the theory." "This," observes Cumings, 
 "may be considered as a fair sample of the general attitude 
 of paleontologists of the Hyatt school. . ." 30 
 
 It was suggested by Hyatt that the conditions for making 
 comparisons between development and the "phylocycle" by 
 means of fossil shells are exceptionally favorable. The shell 
 and its parts are highly significant of the structure of the animal, 
 and display in a unique way the important phases of its growth 
 from the later embryonic stages to old age. Moreover, the 
 procession through geological time is abundantly shown in 
 the successive geological formations not only for the adult forms 
 but for the corresponding immature stages in every youthful 
 phase as well. 31 It is therefore possible for students of these 
 shells to compare immature stages directly with their own adult 
 condition and with the immature and adult conditions of their 
 predecessors and descendants. These favorable circumstances 
 make the conclusions of this group of investigators of peculiar 
 value within the limits of their field of study. 
 
 In making these comparisons Hyatt found certain relations 
 prevailing between the development of the individual and the 
 ancestral series, and summarized them by means of a restate- 
 ment of recapitulation, along with an induction original with him, 
 since known as the law of acceleration. His own words for 
 these two generalizations are: 
 
 •• For a valuable summary of the work of this school, with bibliographies, see an 
 article by this writer, Paleontology and the Recapitulation Theory, in Proceedings of 
 the Indiana Academy of Sciences, 1908-09: pp. 305-340. 
 
 « Phytogeny of an Acquired Characteristic, Proceedings American Philosophical 
 •Society, 1893: p. 350. 
 
24 The Recapitulation Theory and Human Infancy 
 
 "We have endeavored to demonstrate that a natural classifi- 
 cation can be made by means of a system of analysis in which 
 the individual is the unit of comparison, because its life in all 
 its phases, morphological and physiological, embryo, larva, ado- 
 lescent, adult, and old (ontogeny), correlates with the morpholog- 
 ical and physiological history of the group to which it belongs 
 (phylogeny). 
 
 "All modifications and variations in progressive series tend 
 to appear first in the adolescent stages of growth, and then to be 
 inherited in successive descendants at earlier and earlier stages 
 according to the law of acceleration, until they either become 
 embryonic or are crowded out of the organization and replaced 
 in the development by characteristics of later origin." 32 
 
 The term acceleration is not to be understood as implying neces- 
 sarily a quicker development. On the contrary, "an animal 
 having accelerated development of characteristics does not 
 necessarily have a quick development, but may grow, so far 
 as time is concerned, even more slowly than others of its own 
 group." 33 The accelerated characteristic merely takes a new 
 relative position in the whole ontogeny by reason of the omis- 
 sion or suppression of the earliest or older stages and the addition 
 of adaptive phases at the adult end. 
 
 The evolutionary explanation of the law is as follows: 
 
 "We can fully understand the phenomena of acceleration 
 in development only when we begin by assuming that the char- 
 acteristics last introduced in the history of any type were more 
 suitable to the new conditions of life on the horizon of occurrence 
 of the species than those which characterized the same stock 
 in preceding horizons. These characters would then necessarily, 
 on account of their greater usefulness and superior adaptability, 
 interfere with the development of the less useful ancestral stages,, 
 and thus tend to replace them." 34 
 
 Two important additions to this law of acceleration were 
 made by the distinguished American naturalist, Cope, who* 
 presented an independent formulation of the law itself in the 
 year 1866 35 — a year significant for recapitulation, for as has 
 been noted, it gave expression to three original statements of 
 the law, namely, those of Haeckel, Hyatt, and Cope. One of 
 
 " Genesis of the Arietidae, Smithsonian Contributions to Knowledge, 1890, pref- 
 ace 
 
 "IUd., p. 40, footnote. 
 
 "Ibid., pp. 44, 45. 
 
 it Primary Factors of Evolution, 1896, p. 9. 
 
The Recapitulation Theory in Biology 25 
 
 these added ideas was that of unequal acceleration, concerning 
 which Cope makes this statement: 
 
 "The acceleration in the assumption of a character, progressing 
 more rapidly than the same in another character, must soon 
 produce, in a type whose stages were once the exact parallel 
 of a permanent lower form, the condition of inexact paral- 
 lelism. As all the more comprehensive groups present this 
 relation to each other, we are compelled to believe that accelera- 
 tion has been the principle of their successive evolution during 
 the long ages of geological time." 36 
 
 Two other extracts from another writer will show more fully 
 the meaning of this principle: 
 
 "A character useful to the immature form will have a tendency 
 to be inherited at an earlier age than those useful only to the 
 adult, and so by unequal acceleration of development the parallel 
 between ontogeny and phylogeny is broken"; 
 
 and this unequal acceleration is especially to be expected 
 
 "in the larval and adolescent periods where the shortness of the 
 time of development causes throwing together of characters 
 that were not contemporaneous in the ancestors, and where 
 the small size and general habits prevent differentiation of organs 
 that in the correlative adult forms were highly developed. . . "" 
 
 The other idea added to the law of acceleration was named by 
 Cope " retardation.' ' 
 
 "Where characters which appear latest in embryonic history 
 are lost, we have simple retardation, that is, the animal in suc- 
 cessive generations fails to grow up to the highest point of com- 
 pletion, falling further and further back, thus presenting an in- 
 creasingly slower growth in the special direction in question. ' m 
 
 This gives rise to retrogressive series in evolving forms in 
 contrast with progressive series resulting from the effect of 
 acceleration. 
 
 The bearing of these principles of acceleration, unequal ac- 
 celeration, and retardation upon the theory of recapitulation 
 has now to be indicated. If acceleration should operate uni- 
 formly upon lines of descent without obstruction, plainly the- 
 
 " Origin of the Fittest, p. 142. 
 
 •' J. P. Smith, Journ. of Geology, Vol. 8, 1900, p. 417. 
 
 " Origin of the Fittest, p. 13. 
 
26 The Recapitulation Theory and Human Infancy 
 
 ontogeny of a descendant would be a perfectly repeated se- 
 quence of the succession of its adult ancestors, except where 
 the most ancient forms would have been suppressed or omitted 
 from the earliest corresponding embryonic period. This is 
 Cope's "exact parallelism." It would also have the effect 
 of condensing stages without confusing the ancestral order in 
 certain portions of the ontogeny. In case of simple retardation 
 the ontogeny would fail to repeat the most ancient forms, would 
 repeat faithfully the later forms up to the point where the re- 
 tardation left off, and would then fail to repeat stages which 
 the ancestry had recently lost by retardation or successive 
 failure to complete its life cycle. Unequal acceleration would 
 have the effect of "telescoping," or bringing together, stages 
 in ontogeny which had been successive in phylogeny, and to 
 locate later phylogenetic stages before earlier ones. It is ob- 
 vious that, theoretically, this last could confuse the phylogenetic 
 order hopelessly or could even reverse it. 
 
 The relative importance of these several principles, and the 
 validity of recapitulation, becomes therefore a matter of fact. 
 On this point we can but quote competent authority: 
 
 " . . . . there are so many species and genera in the various 
 groups of invertebrates whose ontogeny is simple, progressive, 
 and fairly complete, and whose stages of growth are almost 
 exact repetitions of successive antecedent genera, that it would 
 be impossible to find a student of morphogeny of the brachiopods, 
 the marine mollusks, or the lower crustaceans, that does not 
 believe implicitly in the value of larval stages of these groups 
 as records of their family history." 39 
 
 "In the Cephalapoda, Pelecypoda, Gastropoda, Brachiopoda, 
 Trilobita, Bryozoa, Graptolites, Echinoderms, and Corals, ex- 
 amples are pointed out in which there is clear and unmistak- 
 able evidence of recapitulation." 40 
 
 Hyatt and Cope adduced certain illustrations of accelera- 
 tion and retardation with man and other vertebrates, but since 
 the more recent writers do not emphasize these, it may be as- 
 sumed that the case for recapitulation rests for the group of 
 students here referred to chiefly upon the examples among the 
 invertebrates. 
 
 " J. P. Smith, loc. cit., p. 422. 
 •o Cumings, loc. cit., p. 337. 
 
The Recapitulation Theory in Biology 27 
 
 A point of importance emphasized by Cumings deserves 
 notice here: 
 
 "....the Hyatt school of paleontologists have based their 
 phylogenies on epembryonic [i. e., larval] rather than embryonic 
 stages .... since in the nature of the case the true embryonic 
 stages are scarcely ever accessible to the student of fossils . . . 
 There arises here a question of definition, does the biogenetic 
 law mean that the ontogeny is a recapitulation of the phylogeny, 
 or does it mean that the embryogeny is a recapitulation of the 
 phylogeny?" "In most of these cases [those listed in the second 
 paragraph above] it is the epembryonic and not the embryonic 
 stages that are the basis of comparison. " 41 
 
 In concluding this report of the bearing of acceleration and 
 retardation upon recapitulation, it will be well to refer to a 
 significant caution contained in Cope's discussion of "inexact 
 parallelism." It has been noted that Cope used this expression 
 in part to refer to a lack of correspondence between any ontogeny 
 and its own restricted line of descent. But he used it also to 
 cover a lack of correspondence between an ontogeny of one 
 line of descent and forms in parallel lines of greater or less kin- 
 ship by reason of ancestors at different points of remoteness 
 in the past. Thus, 
 
 "So soon as new subordinate characters are assumed.... 
 the parallelism becomes "inexact," and such is the kind of 
 parallelism usually observed. And it is the more inexact the 
 more widely removed in relationship are the forms compared. 
 Thus the parallelism between the embryo man with five branchial 
 slits, and the adult shark, it is very inexact ; but that between a 
 true fish and a shark is much less inexact. That between a 
 higher and a lower shark is still more exact, and so on." "As 
 we compare species which are more and more different the more 
 necessarily must we confine the assertion of parallelism to single 
 parts of the animals and less to the whole animal." 42 
 
 It appears, therefore, that in the cases of perfect acceleration 
 we have just those conditions required by the logic of the theory 
 of recapitulation in its extreme form. They illustrate nicely 
 the modifications "at a not early age" that Darwin saw were 
 needed for a genetic explanation of von Baer's law, and they 
 fall into Fritz Muller's second class of cases. The evidence 
 
 "Loc. cit.. pp. 306, 337. 
 
 "Primary Factors in Evolution, 1896, pp. 200, 207. 
 
28 The Recapitulation Theory and Human Infancy 
 
 and the authority of the writers quoted in this section leave no 
 question of the actuality of many examples of more or less 
 close recapitulation among the invertebrates, at least for shell 
 characteristics as such, and for whole organisms to the extent 
 shells are illustrative of the entire structure of the animal. 4 * 
 Just how general this recapitulation is does not appear, probab- 
 ly this can not be known as yet. The gist of the contentions 
 of the writers in this field seems to be nothing more than that 
 recapitulation constitutes a working principle for genetic classi- 
 fication of very genuine usefulness. There is no disposition to 
 make of it, at the present time at least, a principle of universal 
 application. It is plain that generalizations carried over from 
 this rather circumscribed field of fact to the vertebrate or 
 human territory, and more especially to the human nervous 
 system or mind, can be the sheerest hypothetical possibilities, 
 in view of the complexity of the facts upon this field of their 
 clearest embodiment and of the possible and probable very un- 
 like conditions that have surrounded the evolution of the high- 
 er vertebrate forms. 
 
 12. The Facts of Recapitulation. 
 
 The sketch of the history of the idea of recapitulation thus 
 far drawn shows that speculation and deduction have had no 
 small part in its formulation. The purpose of the present 
 section is to refer somewhat independently to the facts that 
 have been adduced in its support at different times and by 
 various writers. These facts are found to fall into three classes: 
 (a) those derived from a comparison of known ontogenetic 
 and palaeontological data; (b) those of embryonic resemblance 
 among existing types; (c) t 11 " 00 " f stagPfi oxjeatures in ontogeny 
 
 ^h«3WJQg jesembIanc £jLa-slagfis_or features^so common to lower" 
 allied living groups as to raise- the -question of an ances^al-xer' 
 
 ^ lationship. The facts of the first group are "unequivocal in 
 their significance. Either the parallel exists or does not exist 
 when ontogeny and phylogeny are known and accurately com- 
 pared. The other two types of fact are open to alternative 
 explanations, and give ground for controversy, as we shall see. 
 
 " " The Mollusks would seem, at first sight, bound to supply us with exact phylo- 
 genetic documents by reason of the abundance of their calcerous shells in all geological 
 strata. But. . . the shell is a moiphological organ of little importance." DepSret, 
 loc. cit., p. 48. 
 
The Recapitulation Theory in Biology 29 
 
 (a) The Facts of Palaeontology. 
 
 In the discussion of the views of Darwin reference was made 
 to his expressed sympathy for the belief of Agassiz in the 
 embryonic character of extinct forms. As late as the year 
 1872 Darwin said, "We may hope hereafter to see this law 
 proved true." Commenting on this point an eminent Eng- 
 lish embryologist, Sedgwick, says, "But as Huxley has shown 
 and as the whole course of palaeontological investigation has 
 demonstrated, no such statement can be made. The__§xtinct 
 forms of li fe are ve ry similar to those now existing and there 
 i s nothing specially embryonic about them. So that the facts, 
 as we know them, lend no support to theory."" The reference 
 to Huxley in this quotation is made to papers written in the 
 years 1855 and 1862. In the second paper Huxley wrote "An 
 impartial survey of positively ascertained truth then negatives 
 the common doctrines of progressive modification, or a neces- 
 sary progress from more or less embryonic forms .... it 
 either shows us no evidence of any such modification or demon- 
 strates it to have been very slight." 46 
 
 Passing the question as to whether Huxley's views may have 
 undergone a change of emphasis later with the accession of new 
 facts, we may compare with the statement of Sedgwick the 
 opinions of a distinguished German palaeontologist. Zittel, 
 writing on Palaeontology and the Biogenetic Law, in 1895, says, 
 after referring to the immense advantages that would accrue 
 to palaeontology if this law could be strictly used, 
 
 "If we consult palaeontology, it shows that these surmises 
 are by no means confirmed. There are, indeed, a great number 
 of fossil genera which retain throughout life the embryonic, or, 
 rather, the youthful characters of their existing allies, but it is 
 only among the mammals, and to some extent among the rep- 
 tiles, that I could name a complete series of forms following one 
 another in time and belonging to the same liDe of development. 
 The Eocene, Oligocene, and, in part also, even the Miocene 
 Mammalia stand to their now existing allies, for the most part, 
 in the relation of youthful forms, while they, almost without 
 exception, exhibit at least some characters which are quickly 
 passed through by their geologically younger successors in the 
 embryonic or youthful stage. The ontogeny of organisms now 
 
 « In Darwin and Modern Science, 1909, p. 174. 
 « Scientific Memoirs, Vol. II, p. 528. 
 
30 The Recapitulation Theory and Human Infancy 
 
 living would, for the rest, afford but an unsafe basis for the 
 reconstruction of ancient faunas and floras, since experience 
 teaches that the biogenetic law is frequently veiled or completely 
 obscured owing to various causes." 
 
 Concluding a series of illustrations of the absurdities to follow 
 from an unchecked use of the law this authority remarks that 
 these few instances "may suffice to show how trivial are the 
 discoveries concerning existence in earlier periods of earth- 
 history that can follow from ontogenetic researches alone." 4 ' 
 Cope and others were interested in collecting particular in- 
 stances of recapitulation and these appear in the text-books. 
 They are conveniently presented by Woodward in the follow- 
 ing paragraph: ^f 
 
 "Thpreis nn doubt, for example, that Jrjuthe. course of the 
 in dividual development the'homocercal tail of a.. modern_bony 
 fish passes through .the same, stages as those successively—ex- 
 JSSrfcerMjyjlhe majority of .the_aduU-fishes.at.the-dlffer.ent_ge_o- 
 logi caL epochsT !TJlis^also^y^nt_that _the_fajni|yLi3f jiee^. (Cef- 
 victae) hasgradually acquTred^compIex antlers m precisely the 
 samfi-JiiannerTis-e^^ them "during the 
 
 course cT ltsH K alvidu aT~Tif e . Again" the " "cloven foot"' ' of the 
 eld^tihg^ummant appears-in the embryo with separated meta- 
 podial bones, like those of the adult ancestral ruminants. It is 
 also tolerably certain (though fossils have not yet provided 
 absolute demonstration) that the rudimentary teeth and hind 
 limbs of the existing whale bone whales (Mystacoceti) are in- 
 herited from functionally toothed quadrupedal ancestors." 47 
 
 _In Osborn's "Ev olu tion of Mam maHan Molar Teeth" this 
 example o f recapitula tion- is -io__he_fourid, 
 
 "In the lower molar teeth the order of calcification is precisely 
 
 lAe^HSrSE^SutipiiXr. . . So welind thatjheorder of embryonic* 
 ^development exactly repeatsfne order ofTilstoricaI~development 
 
 . . . .BuL Jhis, ^„is-nol exactly the case in the "upper molars. 
 
 Nevertheless,„x»uLat eight cusps in. the upper and Tower "molars 
 ' considered together, six cusps calcify in the order in whichTBfey 
 
 were successively added to the single reptilian cone." 48 
 
 And from the same authority — this note, 
 
 "The recent discovery of the modes of origin of the horns in 
 the titanotheres, a perissodactyl group remotely related to 
 
 « Natural Science, Vol. 6, 1895: pp. 308, 309. 
 
 «7 Outlines of Vertebrate Palaeontology, 1898, p. xxiii. 
 
 «» p. 65. 
 
The Recapitulation Theory in Biology 31 
 
 horses, tapirs, and rhinoceroses, permits of a comparison of 
 phylogenesis with the ontogenesis of the horns in bovine mam- 
 mals — the conclusion is that ontogeny closely recapitulates 
 phylogeny, that the genesis is gradual or continuous, that the 
 horns arise definitely and determinately."" 
 
 As is well known the ancestry of the horse is one of the few 
 vertebrate ancestries that have been reconstructed on palaeon- 
 tological evidence, and it is therefore of peculiar interest to 
 note the results of a comparison of the embryogeny of the horse 
 with its racial history. This comparison has been made in part 
 by Ewart, who, in the course of his report, raises and answers 
 this question, 
 
 "What evidence is afforded by the horse in favour of the re- 
 capitulation theory? 
 
 Evidently if the reservations made on the plea of abbreviation 
 in development, etc., are almost unlimited, a very remote re- 
 semblance in an embryo to a supposed ancestor might be con- 
 sidered sufficient evidence of recapitulation. . . .There must, 
 however, be some limit to the use of the word recapitulation .... 
 Recapitulation, if it means anything at all, must be held to mean 
 that, say in the case of the horse, the embryo should after a time 
 not only resemble the unknown embryos of its extinct ancestors, 
 but that it should resemble the fully-developed ancestors. This 
 implies that during its ontogeny the horse should not only ad- 
 vance in a zigzag fashion along the trunk of the animal tree, but 
 also when it reached its own particular branch that it should 
 during its onward course make deflections in the direction of 
 Hyracotherium, Mesohippus, etc., until having, at a respectful 
 distance, done hurried homage to its ancestors, it at last reaches 
 its final goal, and presents its true characters .... It is impos- 
 sible with any degree of accuracy, either to speak of a Hyraco- 
 therium or a Mesohippus stage, or even of a Hipparion stage. 
 If, on the other hand, all that is meant by recapitulation is that 
 the developmental record of any given form is represented by 
 a series of zigzags or curves instead of a straight line, the 
 horse may be claimed as supporting it. As is to be expected 
 in forms that have evidently descended from the same ancestors, 
 there is a certain amount of agreement between horse embryos 
 and the so-called fossil horses; and were it possible to know the 
 development of these extinct forms, the points of agreement 
 would be doubtless increased. Further, as might also have been 
 expected, the points of agreement become more numerous and 
 more evident as Hipparion — a not very ancient form — is reached. 
 
 Science, Vol. XXXV, 1912, pp. 595, 596. 
 
32 The Recapitulation Theory and Human Infancy 
 
 So much is this the case, now that we know the second and fourth 
 digits are for a time fairly well developed, we might speak of a 
 Hipparion stage in the ontogeny of the horse. To admit that 
 the horse, before assuming its own specific characters, makes, as 
 it were, a deflection towards the not very ancient form Hipparion, 
 is hardly going far enough to justify the assertion that the horse 
 during its development assumes, one after another, the charac- 
 ters of its ancestors, or, in other words, except in the most limit- 
 ed sense, 'climbs its own ancestral tree.'" 60 
 
 DepeYet, in the book to which reference has already been made, 
 not only presents an authoritative appraisement of the embry- 
 ological method of determining phylogenies, from the viewpoint 
 of palaeontology, but gives also a convenient summary of the 
 amount of correspondence of ontogeny with phylogeny as 
 determined from this same viewpoint: 
 
 "Has Palaeontology completely confirmed the conclusions 
 thus drawn from the embryology of existing beings? We may 
 approach this important question by two different methods. 
 The first method, which is the oldest and the one most generally 
 employed, consists in finding in geological strata forms which in 
 the adult state reproduce one of the transitory phases through 
 which the development of an existing animal passes. We give 
 to these fossil forms the name of Persistent Embryonic types. 
 Palaeontology is able to furnish us with a fairly large number of 
 examples of this. Thus the Fishes of the Primary epoch, such 
 as the scaly Ganoids, have a soft vertebral column in a state of 
 embryonic tissue or notocord, as in the existing Ganoids or Teleo- 
 steans .... In the same way the Palaeozoic Amphibians pass, as 
 regards the ossification of the vertebral column, through a series 
 of progressive phases. . . . These different phases are reproduced 
 in the development of our present Reptiles and Amphibians. In 
 recent and modern Ruminants the bones of the metacarpus and 
 of the metatarsus, separate in the embryo and the young animal, 
 become welded later in the adult into a cannon-bone caused by 
 the fusion of the two metapods. We know among the early 
 Ruminants genera ... .in which the metacarpal and the metatarsal 
 bones remain distinct in the adult state. 
 
 "We may also quote a few persistent types among the Inverte- 
 brates 
 
 "But it must be clearly stated that these examples of representa- 
 tion in fossil adult species of the embryonic, or more correctly, 
 of the youthful characteristics of existing animals, cannot be 
 
 <o Ewart, Journ. Anal, and Phys., Vol. XXVIII, 1893-94, pp. 348-350. 
 
The Recapitulation Theory in Biology 33 
 
 generalized, and that they remain up till now in the state of 
 exceptional facts." 81 
 
 The second mode of answering the question is that of studying 
 the development of fossils themselves, and this has been re- 
 ported in the earlier section dealing with the laws of accelera- 
 tion and retardation. The evidence for recapitulation there 
 presented belongs in character with that just cited. 
 
 With the exception of this last group of facts relating to the 
 shells of invertebrates the authorities quoted are in general 
 agreement. We must conclude that the palaeontological evi- 
 dence for recapitulation is not impressive. Among certain 
 groups of animals in some part of their history, some forms 
 are embryonic in a broad way, and a considerable number of 
 particular instances of the embryonic or youthful retention 
 of ancestral adult traces are noted. Apparently the conditions 
 favoring recapitulation in fossil shells are peculiar to such char- 
 acters. 
 
 (6) The Facts of Embryonic Resemblance. 
 
 The historical importance of von Baer's law for the present 
 topic has been obvious enough. Darwin, Haeckel, and Spen- 
 cer either made it the point of departure of their arguments or 
 drew heavily upon it. Spencer showed clearly in the words 
 quoted from him that a consistent evolutionary application of 
 the law is equivalent to recapitulation. But the limitations 
 of the formula were noticed very early. Darwin alluded to the 
 common, but not invariable, resemblance between embryos in 
 the same class. Fritz Mliller speaks of "developmental forms 
 now so totally different in the nearest allies, now so surpris- 
 ingly similar in members of the most distant groups." 62 Spen- 
 cer regarded the generalization as an average truth only. 
 Haeckel and others found great difficulty in reducing to an order 
 consistent with the law the observed differences between com- 
 parable embryonic stages. The following extracts will indicate 
 the attitude of more recent writers toward the facts in question : 
 
 "Von Baer's statement appears to be erroneous from a modern 
 point of view in the following respects. We know that in certain 
 large groups some forms develop in a very different way from 
 
 Hipp. 254-256. 
 
 n For Darwin, p. 97. 
 
34 The Recapitulation Theory and Human Infancy 
 
 that followed by other members of the group Again, it is 
 
 entirely arbitrary to assume that the group-characters are the 
 first to appear, and then successively those of the order, family, 
 genus, species. Finally .... we do not find early embryos of a 
 group identical, for with a sufficient knowledge of the develop- 
 ment it is always possible to distinguish between the embryos 
 of different species, as well as between adults, only it is more 
 difficult to do so, because the embryonic forms are simpler." 65 
 
 In a study made in 1894 Se dt fopck put_ JhflJaw_io test by 
 .making compa risonsb etween e mbryos of ckjjsely— allied-ammaTs 
 and embry_os_of animals .remotely, related. The observed facts 
 alaTnoTsubstantiate the law/ 4 Sedgwick's more recent state- 
 ment is as follows: 
 
 "The law asserts that embryos of different species of animals 
 of the same group are more alike than the adults and that, the 
 younger the embryo, the greater are the resemblances. If this 
 law could be established it would undoubtedly be a strong argu- 
 ment in favor of the "recapitulation" explanation of the facts 
 of embryology. But its truth has been seriously disputed. If 
 it were true we should expect to find that the embryos of closely 
 similar species would be indistinguishable from one another, 
 but this is notoriously not the case. It is more difficult to meet the 
 assertion when it is made in the form given above, for here we 
 are dealing with matters of opinion. For instance, no one would 
 deny that the embryo of a dogfish is different from the embryo 
 of a rabbit, but there is room for difference of opinion when it is 
 asserted that the difference is less than the difference between 
 an adult dogfish and an adult rabbit. It would be perfectly 
 true to say that the differences between the embryos concern 
 other organs more than do the differences between the adults, 
 but who is prepared to affirm that the presence of a cephalic 
 coelom and of cranial segments, of external gills, of six gill slits, 
 of the kidney tubes opening into the muscle-plate coelom, of an 
 enormous yolk-sack, of a neurenteric canal, and the absence of 
 any trace of an amnion, of an allantois, and of a primitive streak 
 are not morphological facts of as high an import as those implied 
 by the differences between the adults? The generalization 
 undoubtedly had its origin in the fact that there is what may be 
 called a family resemblance between embryos and larvae, but 
 this resemblance, which is by no means exact, is largely superfi- 
 cial and does not extend to anatomical detail." 66 
 
 From these authoritative statements it appears that the 
 facts of embryonic resemblances fail to support recapitulation 
 
 H Morgan, loc. cit., pp. 74, 75. 
 
 m Quart. Journ. of Micros. Sci. Vol. 36, N. S., 1894, pp. 35-52. 
 
 ei Darwin and Modern Science, p. 175. 
 
The Recapitulation Theory in Biology 35 
 
 - >.„.<-»*'•' 
 in all three of its main implications. The order of appearance 
 
 of characters is not uniformly, or even commonly, that required 
 by recapitulation, which is first those representative of the 
 order, and then in succession, of the family, genus, species. 
 In ^he second place, embryonic resemblance in comparable 
 stages does not vary directly with remoteness of kinship, but 
 shows often very great divergence from this rule, indicating 
 unlike careers in lines of descent in the same group and there- 
 fore great diversity in the appearance of variation during de- 
 velopment, at any period, and not only at the adolescent or 
 adult end of ontogeny. Finally, where resemblance does ex- 
 ist, it is not identity, nor even close, implying that the effect 
 of variation upon the same ancestral structure has not been 
 the same in allied lines of descent, but has been productive of 
 new structures, suggesting perhaps in broad outlines the an- 
 cestral structure, but still variant in every case, and essenti- 
 ally so. 
 
 What is left for von Baer's law is the "family resemblance." 
 But family resemblance does not imply recapitulation. It 
 means at most a common ancestor. 66 This common ancestor 
 may have had his ontogeny determined in any way, recapit- 
 ulatory or other. That this family resemblance may often be 
 striking without implying recapitulation is well shown in a 
 recent statement. The Nauplius larva is common to many 
 Crustacea. "But it is not in the least justifiable to deduce, 
 as some have attempted, that the Nauplius larva represents 
 the adult ancestral form from which the Crustacea as a whole 
 have sprung." " The Zoaea larva is similarly characteristic of 
 many widely separated Crustacean groups, nevertheless "it 
 cannot possibly be looked upon as representing the adult an- 
 cestral type of these animals." M 
 
 Again, "A larval form, yet more widely spread than either of 
 the Crustacean larvae mentioned, is the Trochosphere larva, 
 characteristic of Annelids of all kinds and curiously enough of 
 some Mollusks .... which in the adult state are entirely 
 
 ""When we recognize a larval or embryonal form as characteristic for a whole 
 animal group, we may not conclude therefrom that necessarily a similar phylogenetic 
 stage is represented by the same. We are justified only in the conclusion that the 
 ancestral foim of this animal group had possessed that characteristic developmental 
 stage." Hatschek, quoted by Montgomeiy, loc. cit., p. 185. 
 
 « Smith, Primitive Animals, 1912, p. 64. 
 
 " Ibid., p. 65. 
 
36 The Recapitulation Theory and Human Infancy 
 
 different in their whole organization from worms of any de- 
 scriptive. This fact implies that the Trochosphere is an ex- 
 ceedingly ancient type of larva, which must have been possessed at 
 some period by the common ancestor of the Annelids and Mol- 
 lusks . . . There is however nothing to support the view 
 that the Trochosphere in any way represents the common an- 
 cestor of the Annelids and Mollusks. . ."" 
 
 "We cannot however press the argument too far and say 
 that no larval form ever represents an adult ancestral form. 
 Every case must be judged on its own merits after taking into 
 account all the available evidence to be derived from the com- 
 parative study of related forms. Thus it seems indubitable 
 that the so-called Mysis larva, a stage assumed by [many mem- 
 bers of a group of Crustaceans] after the Zoaea .... does 
 very closely represent an adult ancestral form, the actual ex- 
 istence of which is nearly realized by the primitive Anaspides 
 and Schizopod shrimps. Here we are dealing with a late 
 larval form just before the adult structure is attained, and it 
 would appear not to have had time to have been profoundly 
 modified in accordance with larval existence. It would seem, 
 therefore, that we are more likely to meet with actual adult 
 ancestral types in the late larval or developmental stages of 
 fairly closely related animals, which have not had time to be 
 secondarily modified, than in the very early stages of more 
 remotely related forms, although these, in accordance with 
 von Baer's law, may show many points of resemblance which 
 are lost in the adults." 60 
 
 The writer from whom these sentences are taken is able to 
 accept von Baer's law by a loose construction of it: "his [von 
 Baer's] statement was that in any two or more related animals 
 the further back we go in their developmental history from the 
 egg the more do they resemble one another. In this form 
 it must be admitted that von Baer's law holds good with very 
 few exceptions " 61 
 
 This statement may be compared with those of the author- 
 ities already quoted. It appears that even on this loose con- 
 struction of the meaning of von Baer's formulae there is no 
 settled unanimity of opinion among biologists. These dis- 
 crepancies, however, do not affect the essential significance 
 of the law for recapitulation, for as to this all the writers quoted 
 agree in that embryonic likenesses do not of themselves imply 
 
 » Smith, Primitive Animals, 1912, pp. 68, 70. 
 •° Ibid., pp. 66-68. 
 " Ibid., p. 58. 
 
The Recapitulation Theory in Biology 37 
 
 a law of recapitulation, but at most only the retention of ances- 
 tral forms. Whether these are to be regarded as embryonic 
 or adult forms is a matter for study in each case. 
 
 (c) The Facts of Comparative Morphology. 
 
 The third type of evidence for recapitulation, that in volving 
 a comparison of ontogenetic stages with forms commonto "low- 
 * pr" existing groupj ^mav now be referred to. There are, first, 
 those phases in the very early embryonic development of Met- 
 azoa suggestive of a progression from the unicellular condition, 
 and in the development of Chordata, from the simple metazoon 
 form to the chordate and vertebrate condition. The case for 
 recapitulation on these lines is well stated by Dendy in his 
 recent text-book. 
 
 "We have already referred. . . .to some of the earlier stages 
 in the development of that primitive fish-like animal Amphioxus. 
 Let us next enquire how these stages may be interpreted in accor- 
 dance with the recapitulation hypothesis. The unicellular 
 ovum obviously represents the remote protozoon ancestors which 
 were common to the whole animal kingdom, and which are also 
 represented at the present day by independent unicellular or- 
 ganisms such as the Amoeba. The segmentation of the ovum 
 into primitive embryonic cells or blastomeres represents the 
 transition from the condition of the simple protozoon to that of 
 the protozoon colony, in which the individual cells, instead of 
 separating, as in the dividing Amoeba, remain together, but still 
 without undergoing any marked differentiation and division of 
 labor. The arrangement of the blastomeres in the form of a 
 hollow sphere, the blastula or blastosphere, with a single layer 
 of cells surrounding a central cavity, represents the formation 
 of such a protozoon colony as we see in the existing Volvox or 
 Sphaerozoum. The process of gastrulation, whereby the single- 
 layered blastula is converted into a two-layered gastrula, with 
 primitive digestive cavity (enteron) and primitive mouth (blas- 
 topore) represents the transition from the protozoon colony to 
 the coelenterate stage of evolution, the latter being still repre- 
 sented at the present day by such forms as Hydra, Obelia, the 
 jelly-fish, the corals, and all their numerous relations, which 
 retain in their organization all the essential features of the gastru- 
 la, though generally complicated by the development of tentacles, 
 skeleton, etc. The development of the coelomic pouches as 
 outgrowths of the primitive digestive cavity, and the conversion 
 of these into mesoblastic somites, arranged serially or metameri- 
 cally down each side of the body, mark the transition from the 
 unsegmented and coelenterate condition to the metamerically 
 
38 The Recapitulation Theory and Human Infancy 
 
 segmented and coelomate condition. The cavities of the coelo- 
 mic pouches form the coelom or body cavity, which is at first 
 transversely sub-divided into compartments, as it still is in the 
 adult earthworm, while their walls form the third germ-layer 
 or meso-blast, lying between the epiblast which covers the sur- 
 face of the body and the hypoblast which lines the digestive 
 cavity. Along the mid-dorsal line of the body a strip of epi- 
 blast sinks down and becomes folded into the form of a tube, the 
 rudiment of the central nervous system (brain and spinal cord) 
 and beneath this tube a long strip of hypoblast becomes nipped 
 off ffom the roof of the gut, forming the notocord or axial skele- 
 tal rod — the foundation around which in higher types the verte- 
 bral column is built up. A little later the front part of the gut 
 becomes pierced by gill-slits for purposes of respiration and the 
 primitive chordate condition is thus fully attained. 
 
 Amphioxus does not progress much beyond this stage in its 
 development. . . .Amphioxus is a chordate animal but it is not a 
 true vertebrate. It probably, however, represents fairly close- 
 ly a stage of evolution through which the ancestors of the verte- 
 brates have passed, though it becomes somewhat modified by 
 secondary features in the later stages of its development." 62 
 
 In the case of man Haeckel carried the series beyond that 
 represented by Amphioxus through three stages, the cyclostoma, 
 the ichthyoda, and the amniote, making ten stages in all re- 
 presenting an ontogenetic-phylogenetic correspondence. 63 But 
 as suggested above in the account of Haeckel's part in the for- 
 mulation of the theory of recapitulation, the ancestral refer- 
 ence in the higher stages is often to ontogenetic conditions in 
 lower forms, making the adult phylogenetic equivalence in such 
 stages indirect, to say the least. 
 
 It is significant, by the way, that the chief exponent of recap- 
 itulation is able to present an ontogenetic-phylogenetic cor- 
 respondence of ten stages only. When it is considered that on 
 the phylogenetic side the sequence occupied millions of years 
 and proceeded through an almost indefinite number of special 
 forms, the limitations of a conception of ontogeny as illus- 
 trative of the chronological sequence of ancestors become fairly 
 obvious. 
 
 It is almost impossible to report biological opinion as to the 
 significance of the kind of fact now referred to, so various are 
 the views held regarding it. One can merely set the outside- 
 
 '» Outlines of Evolutionary Biology, 1912, pp. 265-267. 
 " Evolution of Man (5th ed. trans.), pp. 547-550. 
 
The Recapitulation Theory in Biology 39 
 
 limits within which it ranges. These are represented at one 
 end by the views of Dendy and Haeckel, as indicated, and those 
 of the palaeontologist, Deperet, at the other. The latter re- 
 fers to Haeckel's hypothetical ancestors as "visions of the 
 mind" because no fossil evidence can be offered for them. 
 It is probably true that most naturalists and embryologists 
 do not wholly discount the phylogenetic significance of the 
 series of early embryonic stages among the Metazoa, and are 
 willing to admit that it may possibly represent in a very gen- 
 eralized fashion what actually happened in the early evolution 
 of organic forms. It may be well, however, to report here a 
 recent conservative statement apparently aimed directly at 
 the type of discussion illustrated in the quotation from Dendy 
 just given: 
 
 " .... in the present state of knowledge we are able to separate 
 the various components of the animal kingdom into a certain 
 number of divergent groups or phyla; and that within the limits 
 of these phyla, although we are far from knowing even approxi- 
 mately in every case the course evolution has followed, yet we 
 are safe in concluding that all the diverse ramifications have 
 originated in the remote past from one common source, or type. 
 But when we attempt to go behind the phyla and discover their 
 origin and inter-relationships, we leave the firm ground alto- 
 gether and wander in a slippery and nebulous region of specula- 
 tion. 
 
 It is true that certain hypotheses of a plausible character have 
 been suggested which have satisfied uncritical minds, and which 
 we often hear advanced as a part of ascertained science and 
 accepted in an otiose spirit. We are urged to believe that life 
 "originated" in certain chemical compounds which on attaining 
 a certain degree of complexity began to exhibit the fundamental 
 properties of life; and from these comparatively structureless 
 masses the nucleated cell was evolved and the unicellular animals 
 and plants, the Protozoa and Protophyta, made their appearance; 
 that these gave rise to cell colonies, the Metaphyta on the one 
 hand, and the Metazoa on the other. The Coelenterate type 
 of organization is presented to us as the form in which the early 
 Metazoa had their being, and from this by the addition of the 
 mesoderm we arrive at the Platyhelmia, and from them by the 
 addition of a coelom and of metameric segmentation at the seg- 
 mented Annelid. And so by the addition and subtraction of 
 their characteristic qualities we may pass in imagination from 
 one fundamental type to another; but what is there of reality 
 in these speculations? They rest not on any objective evidence 
 
40 The Recapitulation Theory and Human Infancy 
 
 but upon the tendency of the mind to pass from the apparently 
 simple to the manifestly complex, and to regard the former as 
 primitive and ancestral and the latter as secondary and deriva- 
 tive."" 
 
 Another class of facts representing this third type of evidence 
 for recapitulation is made up of certain profound metamor- 
 phoses observable in the development of certain groups possess- 
 ing larvae which recall in a rather striking way the ancient 
 forms from which groups in question are believed to be descend- 
 ed. These facts bear unmistakable evidence to a course of 
 evolution in parts of some lines of descent, in which variations 
 or mutations leading to the higher form have supervened em- 
 phatically at the adult end of the ontogeny. Ordinarily these 
 larvae have been adapted in important ways to the special 
 conditions of their life as larvae, but not so seriously as to wholly 
 obscure the ancient structures upon which the adaptations 
 took place. These larval forms are untrue to the ancient 
 pattern also by virtue of the fact that they are transient, con- 
 stantly progressing in the direction of the adult condition, 
 and their organization is therefore disposed in part with refer- 
 ence to the demands of the future. The customary example 
 is the familiar metamorphosis of the common frog. Similar 
 cases are found among the ascidians, the crustaceans, the in- 
 sects, the flat fishes. The only way in which the ancestral 
 reference in these cases is denied is by so minimizing the resem- 
 blance to the ancient form that the recapitulation is said to be 
 wholly superficial and lacking in real significance. This has 
 been done by a few extreme critics of the recapitulation theory. 
 Currect opinion of this class of facts is reported below. 
 
 Finally these are those rudiments and isolated special char- 
 acters in the embryos of higher vertebrates which recall sim- 
 ilar characters and conditions in the adults of lower vertebrate- 
 forms. These are referred to by Sedgwick as follows: 
 
 "... .the embryos of the higher vertebrate possess in the struc- 
 ture of the pharynx and of the heart and vascular system cer- 
 tain features — namely, paired pharyngeal apertures, a simple 
 tubular heart, and a single ventral aorta giving off right and left 
 
 " Smith, Primitive Animals, pp. 14 el seg. 
 
 For an elaborate hypothesis regarding the evolution of animal forms largely on 
 the type of evidence now under discussion, see Bernard, Some Neglected Factors in* 
 Evolution, 1911. 
 
The Recapitulation Theory in Biology 41 
 
 a number of branches which pass between the pharyngeal aper- 
 tures — which permanently characterize these organs in fishes. 
 The skeleton, largely bony in the adult, passes through a stage 
 in which it is entirely without bone, and consists mainly of carti- 
 lage — the form which it permanently possesses in certain fishes. 
 Further, the vertebrate embryo possesses for a time a notocord, a 
 segmented muscular system, a continuity between the pericar- 
 dium and the posterior part of the perivisceral cavity — all 
 features which characterize certain groups of Pisces in the adult 
 state. Instances of this kind might be multiplied for the work 
 of anatomists and embryologists has of late years been largely 
 devoted to adding to them." 86 
 
 There is no disposition evident on the part of biological stu- 
 dents to deny the ancestral reference of this class of facts. Opin- 
 ion differs as to the sense in which they are to be regarded as 
 ancestral. These differences of opinion are reported in the 
 second section following. But it is important to note that 
 such facts coexist with other embryonic conditions for which 
 no ancestral reference is found. For instance, 
 
 "Examples of embryonic characters which are not found in 
 the adults of other vertebrates are the following: At a certain 
 stage of development the central nervous system has the form 
 of a groove in the skin, there is a communication at the hind 
 end of the body between the neural and alimentary canals, the 
 mouth aperture at the first has the form of an elongated slit, 
 the growing end of the Wolffian duct is in some groups continuous 
 with the ectoderm, and the retina is at one stage a portion of 
 the wall of the medullary canal. In the embryos of the lower 
 Vertebrates many other instances of the same interesting char- 
 acter might be mentioned." 66 
 
 IS. Recapitulation and the Physiology of Development. 
 
 The later history of recapitulation has been seriously affected 
 by two lines of thought which combined to unsettle some of 
 its primary assumptions. These followed upon the gradual 
 
 "Encyclopaedia Britannlca, 11th edition, art. Embryology, p. 322. 
 
 <• IUd., 
 
 For a statement of the evidence favorable to recapitulation, see Marshall, Lectures 
 on the Darwinian Theory. 1894, and Biological Lectures and Addresses, 1894, by the same 
 author. Miall's comment on the presentation of Marshall is, "Development tells 
 us something, I admit, and that something Is welcome, but it gives no answer at all 
 to most of the questions we put. . . . The best facts of the Recapitulationist 
 are striking and valuable, but they are much rarer than the thoroughgoing Recapitu- 
 lationist admits; he has picked out all the big strawberries and put them at the top 
 of the basket." Brit. Assoc, for the Adv. of Science, 1897, p. 682. 
 
42 The Recapitulation Theory and Human Infancy 
 
 depreciation of the inheritance of acquired characters which 
 took place in the latter part of the last century, and the appli- 
 cation of experimental methods to the facts of growth and de- 
 velopment (Experimental Zoology, Experimental Embryology, 
 The Mechanics of Development, Experimental Morphology). 
 The inheritance of acquired characters favored a conception 
 of variation at the adult end of ontogeny in response to the 
 direct action of the environment. It was one of the chief in- 
 terests of Hyatt to show how these latest acquisitions in devel- 
 opment became successively inherited in such fashion that 
 they left in the ontogeny a true record of the changes in descent, 
 and it is well known that the three men whose authority gave 
 the greatest prestige to recapitulation, Darwin, 67 Haeckel, 
 and Spencer, all acknowledged the direct action of the environ- 
 ment as a source of variation. 
 
 With tbe progress of the study of development the complex- 
 ity of the whole matter of growth and differentiation of struc- 
 ture became apparent, and the implications for the dominant 
 idea of recapitulation were pointed out. Wilhelm His, in 1874, 
 in "Unserer Korperform," gave expression to his dissatisfac- 
 tion with Haeckel's view of phylogeny as the mechanical cause 
 of ontogeny, and introduced the idea of forces inherent in the 
 process of growth itself to account for its changes of form. His 
 words are as follows: 
 
 "In the entire series of forms which a developing organism 
 runs through, each form is the necessary antecedent step of the 
 following. If the embryo is to reach the complicated end-forms, 
 it must pass, step by step, through the simpler ones. Each 
 step of the series is the physiological consequence of the preceding 
 stage and the necessary condition of the following. Jumps, or 
 short cuts, of the development process, are unknown in the 
 physiological process of development. If embryonic forms are 
 the inevitable precedents of the mature forms, because the more 
 complicated forms must pass through the simpler, we can under- 
 stand the fact that paleontological forms are so often like the 
 embryonic forms of today. The paleontological forms are 
 embryonal, because they have remained at the lower stage of 
 
 ""Whatever Influence long-continued use or disuse may have had in modifying 
 the limbs or other parts of any species, this will chiefly or solely have effected it 
 when nearly mature, when it was compelled to use its full powers to gain its own liv- 
 ing; and the effects thus produced will have been transmitted to the offspring at a 
 corresponding nearly mature age." Origin of Species, II, 6th ed., London, 1902, 
 p. 613. 
 
The Recapitulation Theory in Biology 43 
 
 development, and the present embryos must pass also through 
 lower stages in order to reach the higher. But it is by no means 
 necessary for the later, higher forms to pass through embryonal 
 forms because their ancestors have once existed in this condition" 68 
 
 Haeckel's phylogenetic method is therefore "a mere by-path," 
 and is "not necessary at all for the explanation of the facts of 
 embryology." 
 
 The implications of the germinal origin of variations were indi- 
 cated by Hatschek in these sentences: 
 
 "When one premises (as Haeckel does) that the modifications 
 which the developed individual inherits directly through outer 
 influences become hereditary in its descendants, then the ex- 
 planation shapes itself very simply. The new acquisitions of 
 the adults bring about immediately a prolongation, in the single 
 generation very insignificant, in the course of generations in- 
 creasing, of the ontogenetic row of forms in the descendants. 
 But when one holds fast to the view that only those newly oc- 
 curring characters become inherited, which have arisen through 
 variation of the reproductive cells .... another explanation seems 
 necessary. One must presuppose 'overstepping varieties.' With 
 this name I would call such varieties as consist in a prolongation 
 of the ontogenetic row of forms." 69 
 
 From this conception another seems to follow: 
 
 "We must consider it as a general law, derivable from the 
 principle of causality, that with the phylogenetic modification 
 of the animal form (individual cycle) never only the end stage 
 becomes changed, but always the whole row from egg cell to 
 the end stage. Each modification of the end stage necessitates 
 a change of the egg cell itself." 70 
 
 In view of the truth contained in the last sentence, we must 
 believe that through the course of descent from the unicellular 
 condition to the existing higher species, the germ cell has under- 
 gone an evolution from simple to complicated conditions, cor- 
 responding to the difference in organic complication suggested 
 by a comparison of existing protozoon and highly differentiated 
 adult animals. In what sense, then, can the ovum of a higher 
 vertebrate be said to correspond with the ancestral Amoeboid? 
 
 m Quoted by Morgan, Evolution and Adaptation, p. 71. 
 
 " Quoted by Montgomery. Analysis of Racial Descent, p. 184, from Lehrbuch der 
 Zoologie, 1888. 
 
 '• Quoted by Montgomery, toe. oil. 
 
44 The Recapitulation Theory and Human Infancy 
 
 "Our doctrine is, that the species-cell, even as the adult, 
 many-celled representative of the species, has passed through 
 a progressive, and, indeed, in general a corresponding develop- 
 ment in the course of phylogeny. This view appears to stand 
 in contradiction to the biogenetic law. . . .We must drop the 
 expression 'repetition of the form of extinct forefathers', and 
 put in its place the repetition of forms which are necessary for 
 organic development, and lead from the simple to the complex . . . 
 The egg-cell of the present time, and its one-celled predecessor 
 in the phylogenetic history, the amoeba, are only comparable 
 in so far as they fall under the common definition of the cell, 
 but beyond this they are extraordinarily different .from each 
 other .... Undoubtedly there exists in a certain sense a parallel 
 between the phylogenetic, and the ontogenetic, development .... 
 Ontogenetic studies give us therefore only greatly changed copies 
 of phylogenetic stages. The two correspond not according to 
 their actual contents but only as to their form." 71 
 
 This is the argument and conclusion of the embryologist, 0. 
 Hertwig (1898). Hertwig's concluding idea that the embryo 
 repeats the ancestral stage in its form only does not commend 
 itself to Morgan as a model of clear thinking: "Can we be asked 
 to believe for instance that a young chick repeats the ancestral 
 adult fish form but not the contents of the fish?" 72 
 
 Montgomery was so greatly impressed by these physiological 
 considerations that he was compelled to repudiate recapitula- 
 tion in toto. 
 
 "... .a new racial character is not something, like dead 
 ballast, passively transported by the germ plasm; it is a 
 change in the living processes .... The egg of a Mammal is as 
 dissimilar from that of a Fish as their adult stages, no matter 
 whether the differences are as perceptible or not. This was the 
 idea of the great old-master von Baer; the egg is as much a 
 
 bird as is the hen The earlier the ontogenetic stage the 
 
 more the individual may seem to be like its simple ancestors; 
 but in reality it is just as unlike them in those earlier stages 
 as in its matured condition. For degree of difference must not 
 be adjudged in this case from visible differences alone, but rather 
 equally well from differences in growth energies and ultra-ob- 
 servational structural bases, which, though not perceptible, are 
 nevertheless just as clearly proven to exist. .. .Therefore we 
 can only conclude that the embryogeny does not furnish any 
 
 " Quoted by Morgan, Evolution and Adaptation, pp. 78, 79, 80, 82. 
 "Ibid., p. 83. 
 
The Recapitulation Theory in Biology 45 
 
 recapitulation of the phylogeny, not even a recapitulation 
 marred at occasional points by secondary change." 73 
 
 According to Cumings the error latent in the views of Montgom- 
 ery is the confusion of morphology with physiology. 
 
 " The confusion arising from this source colors all the argument 
 of Montgomery, in which he endeavors to prove that new specific 
 characters must have some representation in the ovum — a view 
 which we must certainly agree with — and that therefore 'the 
 whole row' of cells from the ovum to the adult must be different. 
 We grant that the 'whole row' is different in some way, different 
 in the play of energies; but it may conceivably be morphologi- 
 cally identical up to the very point where the new character 
 is added. It is just as easy to conceive that the energy, or what- 
 ever we choose to call it, that is at a certain stage of development 
 to produce a certain rib or spine or color-band on the shell of a 
 gastropod, may be handed through the row of cells reaching up 
 to the given stage, without producing a single recognizable 
 morphological change in the row, as compared with the individual 
 that is not to possess the new character, as it is to conceive the 
 opposite. The argument for the one view is just as a priori 
 as the argument for the other view. It is also perfectly conceiv- 
 able that the morphology of the individual cells in the row might 
 differ after the acquisition of the new character (in so far as this 
 assumption is required by recent cytological studies), and yet 
 not a single organ or part of the organism be different up to the 
 stage in ontogeny when the new character appears. Unless, 
 therefore, a change in the energies of the cells inevitably neces- 
 sitates a change in the morphology of all the cells or all the organs 
 which they compose, the argument of Montgomery proves 
 nothing." 7 * 
 
 The argument between Montgomery and Cumings apparent- 
 ly labors with difficulties of a logical character as well as with 
 issues of fact, and suggests the desirability of clear concep- 
 tions of the business of intelligence in the presence of the truly 
 genetic phenomena of development. By carrying back in thought 
 to the germ cell all the derivative complexities of the adult, 
 Montgomery succeeds in imputing to it and to all the interven- 
 ing stages a correlative complexity out of keeping with the ob- 
 vious simpler conditions of the earlier ontogenetic stages. By a 
 similar logical extreme Cumings conceives a segregation of the 
 physiological "energies" from the objective morphological 
 
 "Analysis of Bacial Descent, pp. 191, 192. 
 
 " Indiana Acad, of Science, 1908-09, pp. 310, 311. 
 
46 The Recapitulation Theory and Human Infancy 
 
 changes up to the point in development when the new variation 
 appears, when, presumably, the hitherto unrelated "energies" 
 are suddenly connected up with the morphological sequence 
 of events. 
 
 It has been clearly pointed out by the students of genetic 
 logic that in dealing with a genetic series of events the intel- 
 ligence works under constraints which do not hamper it in non- 
 genetic phenomena. A primary obligation laid upon thought 
 in such circumstances is that it shall deal fairly and accurately 
 with the phenomena of any one stage without reading into it 
 what the stage in question may ultimately lead to or what it 
 has proceeded from, except as evidences of these things are 
 actually exhibited in the phenomena. 76 
 
 With these restrictions in mind we may recur to the facts 
 of development as they have been presented by the experi- 
 mental students of the subject. It is worthy of notice that 
 one of the many names applied to the experimental study of 
 development is Experimental Morphology, and it seems evi- 
 dent that in so far as the term "energies," in Cumings's usage, 
 is necessitated by the observed facts it is required in explan- 
 ation of morphological changes, minute and gross, that is, changes 
 of form. A primary dynamic expression, "induction," employ- 
 ed by Driesch, and by Jenkinson after him, is thus defined by 
 the latter: "An 'induction' is simply an effect produced upon 
 the parts that are developing by other parts, or possibly by some 
 factor in the external environment." 76 Perhaps, then, a juster 
 statement of the case would be that inasmuch as latent "en- 
 ergies' ' are known only as they express themselves in the struc- 
 ture and behavior of cells and their aggregates, resemblances 
 and differences in the latter will be the only available index 
 to the resemblances and differences of the "energies" which 
 lie within. Ontogenetic-phylogenetic resemblances, when they 
 have been truly described, therefore, must be regarded as real 
 and not factitious. Moreover, although it must be admitted 
 that the living substance has been greatly modified and differ- 
 entiated through descent, does it follow that it has been utterly 
 made over? If homologies do not refer to essential resemblances, 
 to what can they refer? 
 
 77 See Dewey, Studies In Logical Theory, Ch. I; Baldwin, Development and Evolu- 
 tion, Oh. XIX. 
 
 78 Experimental Embryology, 1909, p. 2. 
 
The Recapitulation Theory in Biology 47 
 
 The question thus becomes one of accurate description, of 
 the greatest difficulty necessarily, in view of the peculiar nature 
 of the facts upon which all inferences as to ontogenetic-ancestral 
 comparisons rest. In the following extract from Minot is pre- 
 sented an illustration of a somewhat closer approach to the 
 comparison than is customary: 
 
 "One of the first things which will impress itself upon the 
 student of vertebrate embryology is, that, though he may find 
 at the proper stage in the embryo the organs of the body clearly 
 developed, yet, owing to the fact that they consist of relatively 
 undifferentiated cells, they are incapable in large part, of per- 
 forming functions which they are ultimately to assume, and the 
 performance of which is the very object of their development. 
 This change in histological structure brings about a marked 
 unlikeness of the embryo to the assumed ancestral type." 77 
 
 The main point of difference between Montgomery and Cum- 
 ings, is, however, not one of logical form merely, but turns upon 
 a significant question of fact. This has to do with the manner 
 in which the specific differences, which by general consent reside 
 n the germ-cell, affect the subsequent course of development. 
 Do these differences express themselves equally upon all periods 
 of ontogeny, and so disturb "the whole row" of stages, as 
 Montgomery implies, or can they be regarded as relatively 
 unimportant in certain phases and highly important in others, 
 as suggested by Cumings? Does a variation affect the entire 
 ontogeny uniformly, or does it exhibit itself at a given period 
 when the conditions are favorable? In short, how much liberty 
 has any phase of growth to evolve by itself without markedly 
 disturbing other phases? 
 
 The facts, as reported by the investigators, seem to favor the 
 suggestion of Cumings. Thus in the language of Driesch, 
 
 "... .the actual fate of a part need not be identical with its 
 possible fate, at least in many cases; . . . . There are more morpho- 
 genetic possibilities contained in each embryonic part than are 
 actually realized in a special morphogenetic case." 78 
 
 That is to say, the fate of a part is determined in some degree 
 in the course of its subsequent history. A complementary 
 thought is embodied in these words of Morgan: 
 
 " Laboratory Text Book in Embryology, 2d ed., 1910, p. 14. 
 
 »• The Science and Philosophy of the Organism, Vol. 1, 1909, p. 77. 
 
48 The Recapitulation Theory and Human Infancy 
 
 "There is certainly no evidence in favor of the view that the 
 organization of the egg need be anything like the organization 
 of the embryo that comes from the egg, although the organiza- 
 tion of the egg may be perfectly definite in its character." 79 
 
 The several "factors" contributing to the differentiation of 
 structure are thus summarized by Jenkinson: 
 
 "Experimental investigation, as far as experiment has at 
 present gone, has shown, first, that a certain complexity of the 
 physical and chemical environment is a necessary condition 
 of normal development; that complexity may, it is true, vary 
 within certain limits, but those limits can only be transgressed 
 under pain of abnormality or death. In the second place, it 
 has been demonstrated that the initial structure of the germ, 
 and the mutual interactions of the parts as they develop are 
 both indispensable factors." 80 
 
 We are thus encouraged to believe that development is neith- 
 er an independent process of self-realization of the germ-cell on 
 the one hand, nor a differentiating effect of a regulative environ- 
 iment upon a neutral protoplasm on the other, but rather an 
 intricate and puzzling interaction or mutual interrelationship 
 of specific external influences and internal conditions. The 
 authoritative primacy of the germ-cell thus becomes greatly re- 
 duced. To recall the usage of von Baer, the egg, the chick, and 
 the hen, the entire ontogeny in fact, is really the bird. The two 
 important ideas for the present discussion of ontogenetic-ances- 
 tral resemblances, to be derived from these considerations, 
 are these: the fate of any embryogeny is in part determined 
 in the course of ontogenetic history, and the succession of 
 events in this history permits a new organization in each phase. 
 This conception of development receives empirical support 
 from the circuitous and indirect course taken by many animals 
 from the germ-cell to the terminal or adult condition. If then 
 the caterpillar is found to have certain describable resemblances 
 to a worm, or a tadpole to a fish, the fact that the subsequent 
 
 ™ Regeneration, 1901. 
 
 •• Experimental Embryology, 1909, p. 279. 
 
 For a summary of the results of experimental study of the effect of environmental 
 differences upon the life cycle, see Morgan, Experimental Zoology, 1910, Chaps. 
 XIX-XXIII. 
 
 A recent significant discussion of the effective relationship of environment to or- 
 ganic existence, is to be found in Henderson, Fitness of the Environment, 1913. 
 A summary statement from this book is the following: ". . . . somehow, be- 
 neath adaptations, peculiar and unsuspected relationships exist between the proper- 
 ties of matter and the phenomena of life." 
 
The Recapitulation Theory in Biology 49 
 
 development leads to a butterfly or a frog need not necessarily 
 be held to discredit these resemblances, and the force of Cumings' 
 contention receives a certain justification. 
 
 That this position has limitations appears from one other 
 aspect of the study of development. Apparently it is possible 
 to over-emphasize the isolation of phases in ontogeny. For 
 although, as Morgan suggests, the organization of one period 
 need not be like the organization of another, still we are told 
 the essential unity of an animal is the central fact of the in- 
 ternal condition of its differentiation of structure, rather than 
 any mere interaction of the parts. This feature of development 
 has led to radical differences of opinion as to its import, and has 
 been interpreted in both vitalistic and mechanical terms. Aside 
 from the matter of interpretation the fact is admitted. The 
 following quotation from Morgan presents the situation as 
 viewed by one student of the facts: 
 
 "The central problem for embryology is the determination 
 of what is the cause, or causes of differentiation. Our analysis 
 leads us to answer that it is the outcome of the organization; 
 but what is the organization?" 81 
 
 The organization .... is a structure or arrangement of the 
 material basis of the organism, and to it are to be referred all 
 the fundamental changes in form, and perhaps of function as 
 well. . . .We know this organization at present from only a few 
 attributes that we ascribe to it, and are not in a position even 
 to picture to ourselves the arrangement that we suppose to 
 exist." 82 
 
 The whole discussion of the section is thus shown to be full 
 of difficulty. We must conclude that the resemblances between 
 ontogenetic stages and ancestral forms are real and not factitious ; 
 still they are resemblances that show themselves among en- 
 tities in some fashion unique in every case. But this seems to 
 be true of all resemblances among organic beings. 
 
 H. Biological Opinion Regarding Recapitulation. 
 
 The situation in biology with reference to recapitulation 
 may be summed up as follows: 
 
 1. Recapitulation as a record of phylogeny is denied in toto. 
 
 2. The traditional view is still upheld. 
 
 81 Regeneration, p. 258. 
 « Ibid., p. 288. 
 
50 The Recapitulation Theory and Human Infancy 
 
 3. The facts are regarded as indicating resemblances between 
 present ontogenies and ancestral ontogenies. 
 
 4. The third view is held, but cases of recapitulation are 
 admitted. 
 
 (1) Montgomery's general denial of recapitulation on phys- 
 iological grounds has been noted and discussed in the section pre- 
 ceding. In an article written in 1897, Hurst takes an equally 
 radical position. 
 
 "... .ontogeny is not an epitome, is not a record, either perfect 
 or imperfect, of past history, is not a recapitulation of the course 
 of evolution." 
 
 Hurst's argument runs as follows: 
 
 "In order that any structure of the adult which varies, and 
 hence ceases to exist as an adult structure at all, may become an 
 ontogenetic record of that adult structure, it is necessary that 
 variation should occur in a way utterly unlike the way in which 
 it does actually occur. The more the adult structure comes to 
 be unlike the adult structure of the ancestors, the more do the 
 late stages of development undergo a modification of the same 
 kind. This is not mere dogma, but is a simple paraphrase of 
 von Baer's law .... 
 
 "In order to produce a 'record' it is necessary that new chapters 
 be added at the end of the pre-existing record. It is necessary, 
 in fact, that as the adult structure varies in one direction, the 
 late stages in development shall vary in another, so as to become, 
 not more like the new adult structure than they were before, 
 but more like the old ones. " 83 
 
 In an article in reply to Hurst, in the same year, Bather makes 
 the following comment upon the former's argument: 
 
 "This is hardly a fair statement of the case. It is not correct 
 to say that the late stages of development must vary in another 
 direction; for it surely is the case, in any series of parents and 
 offspring, which are varying in a given direction, and which we 
 may denote Al, A2, A3, An, that A6 is nearer to A7 than A5 is. 
 Consequently, if the latest stage of development of the form A7 
 resembles A6, it is necessarily more like A7 than a stage that 
 resembles A5. That is to say, on the Recapitulation Theory, 
 the stages of development vary in the same direction as the 
 adults." 84 
 
 Bather substitutes for Hurst's method of variation that of 
 the Hyatt school, with which we are familiar, and then says, 
 
 " Natural Science, Vol. II, 1893, pp. 197, 198. 
 « Natural Science, Vol. II, p. 278. 
 
The Recapitulation Theory in Biology 51 
 
 "Although the adherents of the Recapitulation Theory will 
 doubtless accept the above as, in the main, a correct statement 
 of the method of development, yet not the most sanguine of 
 them will hope to find so perfect an epitome of phylogeny in 
 the majority of cases." It is "truly remarkable that we should 
 get as much recapitulation as we do." 85 
 
 Hurst rested his argument mainly upon von Baer's law and 
 the cases cited in its favor by Darwin, with a few of his own. In 
 his reply Bather refers to cases which point very strongly to 
 an actual retention of adult characters in ontogeny, and ques- 
 tions Hurst's use of von Baer's law. This law was meant to 
 refer to existing groups. 
 
 " . . .there is all the difference in the world between filial and 
 fraternal relationship, and although von Baer's law is undoubt- 
 edly true of the latter, there are many objections to supposing 
 that it is equally true of the former." 
 
 (2) In the section on acceleration and retardation it was shown 
 that many palaeontologists strongly uphold the theory of reca- 
 pitulation and present many illustrative cases especially among 
 invertebrate fossils. That recapitulation in practically the form 
 given it by Haeckel still has advocates appears from the fol- 
 lowing extract of a recent text-book. 
 
 "In short, the embryological investigation of both animal and 
 vegetable organisms leaves no doubt as to the general truth of 
 the recapitulation hypothesis, and must convince any unbiased 
 observer that, however much modified it may be by abbreviation 
 and by the superposition of secondary features, the life-history 
 of the individual is essentially a condensed epitome of the ances- 
 tral history of the race. The law of recapitulation, indeed, may 
 be regarded simply as a logical extension of the law of heredity, 
 for every organism tends to inherit the characters not only of 
 its immediate progenitors but of all its ancestors, and these 
 characters appear in the individual life-history in the same order 
 as that in which they first appeared in the ancestral history — 
 in other words, ontogeny is a repetition of phylogeny and can 
 only be explained in terms of organic evolution." 86 
 
 Perhaps the following quotation from a recent text-book of 
 embryology is more representative of the views of those who 
 still accept recapitulation. It will be noticed that the histor- 
 
 « Natural Science, Vol. II, p. 278. 
 
 »• Dendy, Outlines of Evolutionary Biology, 1912, p. 281. 
 
52 The Recapitulation Theory and Human Infancy 
 
 ical reference is a general one and not to a series of ancestral 
 forms. 
 
 "This repetition is seldom particular, or detailed, never com- 
 plete, yet so many of the phenomena of development can be 
 satisfactorily interpreted from the historical point of view, seem- 
 ing to have this historical sign rather than an immediately adap- 
 tive relation, that as a general statement the law remains funda- 
 mentally true." 87 
 
 (3) The view that the facts upon which the traditional theory 
 of recapitulation has been based can be better explained as indi- 
 cating resemblances between ontogenies of descendants and 
 ontogenies of ancestors has the support of Hurst, Morgan, 
 Sedgwick, Cunningham, Griggs, and others. Of this view 
 Griggs (1909) has this to say: 
 
 "The form which has the largest number of adherents is per- 
 haps that proposed by Morgan ('03), who believes that animals 
 in their ontogeny repeat not the adult, but the embryonic stages 
 of their ancestors. . . .Much of the evidence which the zoologists 
 bring forward in favor of such a modification as against any 
 broader application is so conclusive, one must acknowledge 
 that such is a correct statement of the facts in the particular 
 cases cited, whatever the general law of development may be ... . 
 
 "The evidence presented by the kelps clearly tends to establish 
 the repetition theory of Morgan." 88 
 
 Griggs does, however, find evidence among the kelps of the 
 retention of adult characters, and concludes with a statement 
 favorable to recapitulation. 
 
 Hurst's application of von Baer's law to the disparagement 
 of recapitulation has been given above. His constructive 
 statement from the same point of view follows: 
 
 "Each transient stage in the development of any individual 
 is a modification of the corresponding stage of development of 
 its ancestors. It is in no case a modification of the adult stage 
 of the ancestor. The adult stage of a bird, and no other, cor- 
 responds to the adult stage of the fish-like ancestors (if it ever 
 had such ancestors.) " 89 
 
 Morgan refers to this suggestion of Hurst with approval. 
 His own treatment of the subject under discussion may be 
 
 •' Kellicott, General Embryology, 1913, p. 24. 
 
 88 Kelps and the Recapitulation Theory, Amer. Naturalist, Vol. 43, 1909, p. 97. 
 
 •• Loc. cit., p. 199. 
 
The Recapitulation Theory in Biology 53 
 
 summarized. Passing in review the most prominent of the 
 cases that have been offered in support of recapitulation, namely, 
 the gill-clefts of reptiles, birds, and mammals, the notocord in 
 the vertebrate series, the development of the skull, of the kid- 
 neys, of the heart, with some others, and noting in some de- 
 tail in each case the likeness of the ontogenetic formation to 
 the corresponding conditions and functions at different levels 
 in the chordate series, he is impressed by the following facts. 
 Certain differentiations, such as external gills in the tadpole, 
 do not seem to have any representation among adults in the 
 lower groups. Such transformations as those of the tadpole, 
 can only be regarded as at best analogous to ancestral transi- 
 tions. More especially, the gill-clefts appear as early in the 
 development of the mammal as in the salamander or fish, which 
 seems paradoxical if the appearance in the mammal is a repeti- 
 tion of the adult amphibian stage. The case is not greatly 
 different with the notocord, skull, kidneys, and heart. Again, 
 in the cases of rudimentary teeth in birds, whales, and other 
 animals, it is manifestly absurd to claim that the ancestral adult 
 condition is repeated when rudiments only appear. Finally, 
 the possible complete loss of ancestral stages is shown in the 
 lack of any indication in the ontogeny of the snake of the limbs 
 of its lizard-like ancestors. Cases of the repetition of adult 
 ancestral stages outside the group of vertebrates, he avers, are 
 often doubtful, sometimes little less than fanciful. Moreover, 
 the work of certain students among the invertebrates shows that 
 common embryonic forms are found which could not possibly 
 be regarded as due to the retention of adult ancestral forms. 
 
 How, then, are the apparent resemblances between the em- 
 bryos of higher forms and the adult of lower animals to be ex- 
 plained? 
 
 "The answer is that this resemblance is deceptive, and in so 
 far as there is a resemblance it depends on the resemblance of 
 the adult of the lower form to its own embryonic stages with 
 which we can really make a comparison. The gill-slits of the 
 «mbryo of the chick are to be compared, not with those of the 
 adult fish, but with those of the embryo of the fish. . . .It is 
 only the embryonic stages of the two groups that we are justified 
 in comparing; and their resemblances are explained on the as- 
 sumption that there has been an ancestral adult form having 
 these embryonic stages in its development and these stages 
 
54 The Recapitulation Theory and Human Infancy 
 
 have been handed down to the divergent lines of its descend- 
 ants." 90 
 
 In the opinion of Sedgwick the facts implying an ancestral 
 reference have been much exaggerated, but a sufficient number 
 of unequivocal cases do exist to require explanation. His ex- 
 planation follows: 
 
 "A disappearing adult organ is not retained in a relatively 
 greater development by an organism in the earlier stages of its 
 individual growth unless it is of functional importance to the 
 young form. In the cases in which the whole development is 
 embryonic this rarely happens, because the conditions of em- 
 bryonic life are so different from free life that functional embryon- 
 ic organs are usually organs sui generis, e. g., the placenta, am- 
 nion, etc., which cannot be traced to a modification of organs 
 previously present in the adult. It does, however, appear to 
 have happened sometimes, as an instance of it may be mentioned 
 the ductus arteriosus of the Sauropsidan and Mammalian 
 embryo. On the other hand, when there is a considerable period 
 of larval life, it does appear that there is a strong case for thinking 
 that organs which have been lost by the adult may be retained 
 and made use of by the larva. The best known example that 
 can be given of this is the tadpole of the frog. Here we find 
 organs, viz., gills and gill-slits, which are universally regarded as 
 having been attributes of all terrestrial Vertebrata in an earlier 
 and aquatic condition, and we also notice that their retention 
 is due to their being useful on account of the supposed ancient 
 conditions of life having been retained. Many other instances, 
 more or less plausible, of a like retention of ancestral features 
 of larvae might be mentioned, and it must be conceded that 
 there are strong reasons for supposing that larvae often retain 
 traces, more or less complete, of ancestral stages of structure- 
 But this admission does not carry with it any obligation to ac- 
 cept the widely prevalent view that larval history can in any 
 way be regarded as a recapitulation of ancestral history. Far 
 from it, for larvae in retaining some ancestral features are in no 
 way different from adults; they differ only from adults in the feat- 
 ures which they have retained. Both larvae and adults retain an- 
 cestral features, and both have been modified by an adaptation 
 to their respective conditions of life which has ever been becom- 
 ing more perfect. 
 
 The conclusion, then, has been reached, that whereas larvae 
 frequently retain traces of ancestral stages of adult structure, 
 embryos will rarely do so; and we are confronted again with 
 the question, How can we account for the presence in the embryo* 
 
 so Evolution and Adaptation, pp. 73, 83. 
 
The Recapitulation Theory in Biology 55 
 
 of numerous functionless organs which cannot be explained other- 
 wise than as having been inherited from a previous condition 
 in which they were functional? The answer is that the only 
 organs of this kind which have been retained are organs which 
 have been lost by the adult and have become in this way im- 
 pressed upon development. As an illustration taken from cur- 
 rent natural history of the manner in which larval characters 
 are in actual process of becoming embryonic may be mentioned 
 the case of the viviparous salamander (Salamander atra), in 
 which the gills, etc., are all developed but never used, the animal 
 being born without them. In other and closely allied species 
 of salamander there is a considerable period of larval life in which 
 the gills and gill-slits are functional, but in this species the larval 
 stage, for the existence of which there was a distinct reason, viz., 
 the entirely aquatic habits of life in the young state, has become 
 at one stroke embryonic by its simple absorption into the em- 
 bryonic period. The view, then, that embryonic development 
 is essentially a recapitulation of ancestral history must be 
 given up; it contains only a few references to ancestral history, 
 namely, those which have been preserved probably in a much 
 modified form by previous larvae. "" 
 
 This lengthy quotation may be brought to a point by a con- 
 crete application. The traces of gill-slits in the human embryo 
 mean that at a certain period in geological time one of the ances- 
 tors of man was an animal with a larva possessing functional 
 gills of use to it in the water. Later with the extension of the 
 embryonic period this functional condition was rendered use- 
 less by being absorbed, that is, taken into the egg or body of 
 the mother before birth. Its subsequent embryonic history 
 greatly modified it and reduced it to a rudiment. 
 
 It appears, therefore, that with reference to ancestral traces 
 among embryos Sedgwick agrees in the main with Hurst and 
 Morgan. These traces are due to the transmission of similar 
 embryonic forms through successive generations. But Sedgwick 
 differs from these writers in that he does believe there are a 
 few cases of the embryonic retention of functional adult char- 
 acters. And he differs radically in the belief that larvae often 
 retain adult characters in continuing in the life conditions of 
 their ancestors. This however does not happen in a way to 
 show recapitulation. Sedgwick goes beyond Morgan in sug- 
 gesting how the ancestral form originally got the adult char- 
 
 " Encyclopaedia Britannlca, 11th ed., art. Embryology, p. 323. 
 
56 The Recapitulation Theory and Human Infancy 
 
 acter which was carried down through embryogeny in descent. 
 This, it will be recalled, Morgan did not attempt to explain. 
 This hypothesis of Sedgwick 92 was accepted and applied by 
 two other biologists. Cunningham carried the discussion back 
 to the probable ancestor of the Amniota to which the larval 
 condition may be assigned. It is not likely, he says, that the 
 case of Salamander atra is illustrative of the absorption of the 
 branchiate condition among mammals, 
 
 "Since viviparity even in Mammals was evidently acquired 
 at a later stage, and the change came about by means of the 
 development of an egg-shell in which the larva was contained 
 and protected during its development." Moreover, "the mere 
 fact that they were functional originally in a free larval condi- 
 tion is probably not the whole explanation of the temporary 
 development of a complete system of gill-arches and gill-slits 
 in the amnoite embryo. Supposing that no functional import- 
 ance in embryonic life belongs to them, it is to be noted that the 
 embryonic branchial blood vessels are metamorphosed into the 
 vascular system of the adult, as they are in the metamorphosis 
 of the Amphibia, and a very considerable and very important 
 part of them persists in the adult structure. This does not ac- 
 count for the persistence in the embryo of open branchial clefts, 
 but even these do not wholly disappear in development. The 
 first remains as the Eustachian tube, and even the posterior 
 are related to the thymus gland. It seems to be a general fact 
 that a structure which in metamorphosis disappears completely 
 may easily be omitted altogether in embryonic development, 
 while one which is modified into something else continues to 
 pass more or less through its original larval condition. If the 
 aquatic larval condition then was ever an adult ancestral con- 
 dition it must have been the ancestor of Amphibian forms, and 
 only through these the ancestor of the Amniota." 93 
 
 The adapted character of these larval forms which reflect in 
 some degree an ancient adult condition is made clear by Cunning- 
 ham, and is of special significance for this whole class of recapitu- 
 latory cases. From a comparison of the tadpole and the known 
 forms of fishes he concludes that 
 
 "The larva of the frog, therefore, instead of recapitulating 
 the ancestral condition has lost nearly everything characteristic 
 of a fish except the pharyngeal branchiae, which it could not 
 
 •> Cunningham notes that the same suggestion was made antecedently by Bal- 
 four. See Comparative Embryology, 2d ed., 1885, p. 210. 
 " Science Progress, VI, 1897, p. 488. 
 
The Recapitulation Theory in Biology 57 
 
 lose without ceasing altogether to be an aquatic larva. The 
 larva is therefore much more of an adaptation than a recapitu- 
 lation." 31 
 
 This he finds generally true of flat fish and other animals with 
 such larvae, so that he feels warranted in making the statement 
 that "Recapitulation does not occur. . . .except when the extern- 
 al condition to which the ancestral structure was adapted con- 
 tinues to act at an early period of life." 95 
 
 Macbride, employing Sedgwick's theory, gives many illus- 
 trative cases and compares the conditions of larvae and embryos. 
 Ancestral traces are found in the vast majority of larvae. 96 
 
 (4) We are thus led to the fourth position assumed toward 
 recapitulation. It is close to that of Sedgwick just described. 
 The greater part of the resemblance between descendants and 
 ancestors is, where it exists at all, between their ontogenies. 
 Nevertheless, cases exist, more especially among larvae, of the 
 ontogenetic retention of adult characters. This, it is to be 
 noted, agrees with the results of the Hyatt school of palaeontol- 
 ogists. In their impressive array of facts, as summarized by 
 Cumings, it was the post-embryonic and not the embryonic 
 stages that made the basis of comparison. 97 
 
 Grigg's acceptance of both the view of ontogenetic repetition 
 and that of ontogenetic-adult repetition, has been noted. A 
 sentence from this writer will serve as a fitting conclusion to 
 this report of opinion: "In each case the evidence must be 
 weighed before a conclusion can be reached." 
 
 15. Summary and Conclusions. 
 
 The history of the recapitulation theory may be briefly re- 
 viewed. In the early references to the idea at the beginning 
 of the nineteenth century, when the science of embryology 
 was taking form, the attention of observers was caught by re- 
 semblances which evoked the belief that individual develop- 
 
 « Science Progress, VI, 1897, p. 489. 
 
 " Ibid., p. 508. 
 
 The functional character of embryonic and rudimentary embryonic structures is 
 illustrated and enlarged upon by Peter, Ueber die biologische Bedeutung embryonaler 
 und rudimentSrer Organe, Arch, fur Entwickelungsmechanik, 1910. 
 
 " Sedgwick's Theory of the Embryonic Phase of Ontogeny, etc., Quart. Journ. 
 Micros. Sci., XXXVII, 1894-95. 
 
 'i See page 27. 
 
58 The Recapitulation Theory and Human Infancy 
 
 ment displayed in succession the forms of animals as they 
 ranged in a single series one above the other. In one instance 
 this was regarded as a rehearsal of the story of creation of these 
 forms (Oken). Von Baer's suggestion that the prevailing idea 
 was an error and that the resemblances were between embryos 
 of the four great types, to be detected among animals, was for 
 the time disregarded, in favor of a conception of Agassiz of a 
 parallelism between the succession of geological forms as in- 
 dicated by fossils and the succession of stages in development, 
 a parallelism expressive of one feature of the divine plan of cre- 
 ation. With the advent of the theory of descent with modi- 
 fication the facts of the older view were invoked in support of 
 the theory, and Darwin, with the help of Fritz Miiller, showed 
 how a genetic classification could be determined in large part 
 with the aid of embryology. Darwin's moderate acceptance 
 of the theory of a developmental rehearsal or recapitulation of 
 racial history, was supplanted by the radical statements of 
 Haeckel, who, by misconceiving the effects of heredity and 
 adaptation through successive generations, formulated a "bio- 
 genetic fundamental law," which implied that by necessity on- 
 togenies must preserve an abbreviated and condensed record 
 of ph3"logeny. Herbert Spencer helped to extend the influ- 
 ence of this view by accepting it in general, while showing in 
 some detail its limitations. Recapitulation derived new war- 
 rant from a series of important investigations made by Hyatt 
 and his followers upon fossil shells of some invertebrates, which 
 showed how by the acceleration and retardation of adult char- 
 acters in ontogeny a record of the phylogeny was preserved. 
 The palaeontologists of this school to-day constitute the chief 
 advocates of the views of recapitulation as supplying a fairly 
 faithful record of phylogeny in many cases. Among the embry- 
 ologists the ancestral record in ontogeny was acknowledged 
 and employed for a considerable period until absurdities due 
 to its extreme application greatly impaired its prestige. At 
 the present time the weight of authority favors an explanation 
 of established ancestral traces in ontogeny as being due to 
 the transmission of similar embryonic and larval conditions 
 through successive descendants, while admitting the retention 
 of adult characters in ontogeny in some instances. These traces 
 are not such, however, as to present in any real sense a chrono- 
 
The Recapitulation Theory in Biology 59 
 
 logical record or recapitulation of the evolution of the race 
 through descent. Several biologists believe that the origin of 
 embryonic traces of adult ancestral forms is due to an extension 
 of the embryonic period to include characters once functional in 
 larvae, these characters having been retained by the larvae when 
 no longer needed by the modified adult. The genuineness of 
 ancestral resemblance has been impugned on physiological 
 grounds, but the justification for this seems questionable when 
 the facts are carefully described. 
 
 Conclusions Regarding Recapitulation. 
 
 The above account of the biological discussion of recapit- 
 ulation seems to lead to the following conclusions: 
 
 1. Ontogeny denotes the sequence of events in the life-history 
 of the individual beginning with the maturation and fertiliza- 
 tion of the egg, and progressing, under the stimulation of the 
 environment and the mutual relation of parts, through a series 
 of structures to senility and death. 
 
 2. A proper conception of an animal involves the entire life- 
 history and should not be based upon its adult condition alone. 
 There has been some kind of life-history from the beginning. 
 "Development and life are coextensive." 98 
 
 3. Heredity denotes the persistence of characteristics through 
 descent, whereby the life-history tends to be preserved in its 
 original form. 
 
 4. But the several phases or periods of ontogeny (embryonic, 
 larval, adolescent, adult, senile) are all subject to variation, 
 and selection (when they are such as to be affected by biolog- 
 ical utility) and have varied in unlike degrees, whether one 
 compares stages in one line of descent or homologous stages 
 in different lines of descent. 
 
 5. These variations, whether small or greater, have appeared 
 in, upon, and around old structures, so that any phase of on- 
 togeny undergoing revision tends to preserve in some degree 
 the character of the original basic structure. Because of this 
 fact any ontogeny is likely to give some indication of its past, 
 and to this extent constitutes a "record." 
 
 6. Resemblances between comparable ontogenetic periods 
 will therefore tend to be closest between descendants and im- 
 
 98 Cf . Sedgwick, in Darwin and Modern Science. 
 
60 The Recapitulation Theory and Human Infancy 
 
 mediate ancestors. They will on the whole decrease with the 
 widening of the interval between the ancestors and descendants 
 compared. 
 
 7. The millions of years occupied by any line of descent has 
 given opportunity for every degree of reconstruction of the life- 
 history to the most radical and it is surprising that a later 
 ontogeny should preserve any traces whatever of the life-history 
 of remote ancestors. 
 
 8. In many groups there are very few, if any, such traces, 
 the life-history showing from an early period only the features 
 of its present adult condition. 
 
 9. In other groups the life-history is not direct but circui- 
 tous, and presents forms which require an explanation other 
 than that of adaptation to the environmental conditions of the 
 adult. These forms often have some kind of ancestral refer- 
 ence, and have been retained probably because of some utility 
 either to the larvae in their independent struggle for existence, 
 or as structural bases for higher differentiations in case they 
 are found in embryos. Some are rudiments without utility 
 of any discernible sort. 
 
 10. In the majority of cases the ancestral reference of embry- 
 onic or larval stages is to embryonic and larval stages of ances- 
 tors. These may have originated either as larval or embryonic 
 conditions as such, or as adult structures which have been re- 
 tained in some fashion in the earlier ontogeny of descendants. 
 
 11. In the smaller number of cases where the ancestral refer- 
 ence of early ontogenetic stages is conclusively to adult forms 
 the explanation is as follows : A life-history originally direct may 
 have been modified at a not early age and thus left the earlier 
 part to resemble the adult ancestor. If this should have happen- 
 ed successively so that modifications each time came later than 
 the already acquired modifications, the later stages in the devel- 
 opment of descendants would indicate something of the sequence 
 in which the modifications were successively added in the phy- 
 logeny. These stages would then "recapitulate " that part of the 
 phylogeny during which the modifications took place in this 
 fashion. If the modifications had been made uniformly in this 
 way, then the whole ontogeny would present a "recapitulation" 
 or chronological record of phylogeny, except where suppression, 
 consolidation, unequal acceleration, and retardation had inci- 
 dentally prevented. 
 
The Recapitulation Theory in Biology 61 
 
 12. It is obvious that recapitulation in the sense of a chrono- 
 logical repetition of a succession of adult forms in phylogeny is 
 very unlikely. It may have happened in the earliest evolu- 
 tion of organic form as suggested by the very general 
 similarity in early ontogenetic development of the Metazoa, 
 a development which has a somewhat general corre- 
 spondence to what is believed by many to be the evolu- 
 tionary sequence among existing lower forms. It has happened 
 somewhat conspicuously among many animals with larvae, 
 for a certain part of the life-history, and also with particular 
 characteristics and organs in some degree, more noticeably in 
 shells and bony structures. 
 
 13. But where such recapitulation has occurred, there has 
 been coincidently an alteration of the ancient structures, so that 
 the original form of the latter is often made out with great 
 difficulty, the alteration having had the effect of obscuring the 
 older pattern to some degree, often radically. As a conse- 
 quence life-history has been very much more altered than it 
 has been extended through descent. 
 
 14. If by recapitulation is meant any traces of adult features 
 in early ontogeny, there is considerable evidence for it, although 
 not a large amount comparatively. But this is not recapitu- 
 lation in the proper meaning of the term. If by recapitulation 
 is meant any ancestral reference whatever in early ontogeny, 
 there is much of this, especially to more recent ancestral life- 
 history, but this is even a farther remove from the meaning of 
 the word. It is practically synonymous with heredity. If 
 ontogeny is a "record" at all, it is more particularly a record 
 of antecedent ontogenies, to the degree these are not effaced 
 by subsequent variational or mutational changes. 
 
CHAPTER III 
 
 HUMAN INFANCY AND THE RECAPITULATION 
 THEORY 
 
 1. Human Embryogeny. 
 
 The ancestral significance of the facts of human foetal develop- 
 ment was carefully considered by Duckworth in "Morphology and 
 Anthropology" (1904). This author made comparisons with 
 respect to external features, topographical and systematic ana- 
 tomy, between the human foetus at birth, also at a point about 
 half way through embryonic development, and the human adult 
 and existing primates. His conclusions are briefly as follows. 
 With respect to the external features of the human foetus a 
 small number of simian characters are recognizable in both 
 stages studied, although the younger stage does not show these 
 in any greater frequency. This is practically the result of the 
 comparison based on topographical anatomy. Some of the 
 points of difference from the adult human condition constitute 
 resemblances to conditions obtaining among the primates. No 
 special primate form is indicated. The conclusions regarding 
 systematic anatomy are given in the words of the author. The 
 observations regarding the ninth month foetal stage are arranged 
 with respect to descent in three groups. 
 
 "First of all, there are to be noticed characters, such as the 
 relatively large size of the liver, of the hypogastric arteries, or 
 of the fontanelles, which appear to be quite irrelevant; these are 
 in fact, conditions associated with, and determined by the par- 
 ticular and peculiar mode of development in the higher Eutheria, 
 and, therefore, they may be expected to obtain in all these 
 animals alike. Secondly, there are a number of characters, 
 such as the great size of the head and of the cerebrum, which 
 are related to the specific and peculiar characters of the Homin- 
 idae, and which might well be expected to be so impressed in 
 their organization as to appear prematurely, so to speak, in his 
 individual development. . . . These two classes constitute 
 a very considerable number of characters which do not bear 
 upon the question of descent and must be carefully eliminated. 
 
 62 
 
Human Infancy and the Recapitulation Theory 63 
 
 "... there remains a residue . . which may be collected 
 and associated in a category of pithecoid affinities. The flat- 
 ness of the nose, the imperfect power of opposition of the pollex 
 (shown by the mode of grasping in the new-born infant), the 
 straighter lumbar column, the flattened sacrum, the imperfectly 
 extensible hip and knee, the proportionately long upperlimb, 
 the incurved feet (and, in the female, the straighter vagina), 
 may be mentioned as features of this kind . . . further 
 . . . there is no reasonable doubt but that the associations 
 are with the Simidae rather than with their lower congeners 
 among the Primates." 1 
 
 The foetus at the fifth month shows a somewhat greater 
 prominence of the features associated with placental development 
 as such, and the specific human characters are asserting them- 
 selves. The residue of simian characters is very small, so small 
 indeed, that nothing is indicated of man's ancestry beyond the 
 immediately antecedent Simidae. 
 
 It will be seen from this authoritative review of the facts of 
 foetal development that the character of the human foetus is 
 determined chiefly by its particular foetal condition and by its 
 future as an adult human organism. The resemblances to adult 
 existing apes, and presumably to the adult ape-like ancestor, 
 are few and comparatively unimportant, and as far as we can 
 see, are such as might be due to an indirect likeness to this ape- 
 like ancestor by way of the foetus of the latter. This accords 
 with the view of ancestral similarities reported in the preceding 
 chapter as that having the greater weight of authority among 
 biologists. In instituting these comparisons between non- 
 comparable stages, that is, between the human foetus and the 
 adult ape, Duckworth is under the influence of the traditional 
 conception of recapitulation, to which he refers sympathetically 
 in his introductory paragraphs. 
 
 In the chapter following (VIII) the author reports the results 
 of a comparison of certain features in the mode of development of 
 man and the apes in the earlier stages. As we should now expect 
 when corresponding ontogenetic stages between closely allied 
 forms are compared, a striking resemblance is found. And, as we 
 should also expect, the resemblances, though more often with 
 the embryogeny of the ape, are to a less degree, with other and 
 lower mammals. The closeness of this correspondence between 
 
 'pp. 188, 190. 
 
64 The Recapitulation Theory and Human Infancy 
 
 ontogenetic stages, together with the comparative lack of it 
 between the human foetus and the adult condition among apes, 
 once more tends to illustrate the fallacy of the traditional view 
 of recapitulation and to yield added support to the substituted 
 conception of ontogenetic correspondence between descendants 
 and immediate ancestors. A study 2 of the degree of likeness 
 of a foetal gorilla to the human foetus made by the same writer 
 seems to agree with this view, although the author is more 
 interested in indicating the distinguishing characteristics. 
 Human traits are quite plainly manifested in early foetal stages.* 
 
 2. The Theory of Infancy. 
 
 The life-history of the higher mammalia, like that of many 
 lower vertebrate and invertebrate groups, is characterized by a 
 period intervening between the close of embryogeny and the 
 full assumption of adult structures and functions. But whereas 
 larval forms are compelled by the necessities of their independent 
 life to provide themselves with food and protection during the 
 progress of their maturing, the corresponding period among the 
 higher mammalia is one in which the processes of growth and 
 increasing maturity are largely freed from such necessities by 
 the care and protection of a parent or parents. 
 
 The term infancy has been applied to this period and an ex- 
 planation of it in terms of biological utility has become current, 
 associated especially with the name of the American philosopher 
 and historian, John Fiske. In the address on the subject printed 
 in "Century of Science " Fiske deals reminiscently with the incep- 
 tion of the theory. He recalls that the impression left upon the 
 minds of many from the reading of Darwin's "Descent of Man" 
 in 1871 was in some ways unsatisfying. Although Darwin's 
 work presented an impressive array of instances of similarity be- 
 tween man and the animals, still the method of the transition 
 to an essentially human condition was not clearly elucidated, 
 and there was a consequent confusion as to man's future destiny 
 as determined by the Darwinian factors of species evolution. 
 
 'Studies In Anthropology, 1904. 
 
 'Ontogenetic likeness is affirmed in current statements of an "almost appalling 
 resemblance between man and the ape before birth," a resemblance which is 
 asserted to be much closer than that between adult man and adult ape. See Mitchell, 
 Childhood of Animals, pp. 7-9 ; von Buttel-Reepen, Man and his Forerunners, trans., 
 1913, p. 76. 
 
Human Infancy and the Recapitulation Theory 65 
 
 A significant suggestion which was to lead to a better under- 
 standing of this transition, had already been made in an essay- 
 by Wallace, Darwin's co-discoverer of the descent theory. This 
 essay appeared in 1864, 4 and presented the idea that for a long 
 period in the history of man's immediate ancestors natural 
 selection had been slowly transferring from the body to the mind, 
 so that by the time of the final emergence of the human species 
 man's bodily evolution had been practically completed for all 
 time, his future evolution being destined to take place along 
 intellectual and moral lines. That is to say, the transition from 
 the ape-like to the human condition had been chiefly in the 
 region of mind and the nervous system. 
 
 It is in this connection that Fiske's theory of infancy became 
 prominent. Fiske's thought in this direction was taking form as 
 early as the year 1873, as we learn from a paper published in the 
 North American Review for that year. A more complete state- 
 ment appeared in the Cosmic Philosophy of 1875, an independent 
 and constructive presentation of the Spencerian philosophy for 
 American readers. Fiske's views were reiterated with insigni- 
 ficant modifications in his later writings. 5 
 
 The argument of the theory runs as follows. There is an 
 increase in the amount of nerve tissue of the cephalic ganglia, 
 and in the convolutions of the cerebral surface, paralleled by an 
 increase in the higher psychical powers, in the vertebrate scale 
 from lower to higher forms. These higher powers are associated 
 with the compounding and co-ordinating of already compounded 
 nerve connections in the lower centers. Whereas among the 
 lower vertebrates the uniformity and repetition of identical 
 responses to environment brings about a fixed and determined 
 reflex and instinctive organization of nerve tracts in the individu- 
 al, which are transmitted to descendants, the responses of higher 
 vertebrates are so complex, so lacking in uniformity, that repeti- 
 tion of any specific mode is insufficient to fasten upon the indi- 
 vidual and his descendants fixed modes of action. There arises 
 accordingly among such animals a plastic condition of the higher 
 nerve connections which requires time in the early years of life 
 
 « Reprinted in Natural Selection and Tropical Nature, chap. VIII. 
 
 « Vol. II, Chap. XVI and XXII. For later statements, see Excursions of an Evolu- 
 tionist, Chap. XII; Destiny of Man, 35-76. Anticipations of Fiske's idea have been 
 pointed out by Butler, Armstrong, and others. See Phil. Ben., Vol. 15, p. 59. 
 
66 The Recapitulation Theory and Human Infancy 
 
 for their exercise and adult determination, and brings with it 
 coincidently a corresponding amount of helplessness on the part 
 of the young, demanding parental care and protection. Con- 
 sciousness is especially associated with these complex and intri- 
 cate connections of the higher ganglia, and very little or not at 
 all with the mechanical reactions of the lower centers. Thus 
 arises conscious intelligence with its differentiation in emotion, 
 memory, perception and reasoning, and volition. In the case 
 of man this whole evolution has reached its acme, so that brain 
 tissues are largest, convolutions of the cerebral surface are most 
 noticeable, the highest psychic powers are manifested, the period 
 of infancy is longest, and parental solicitude most intense. The 
 process has been continued from savagery to civilization. Paren- 
 tal care first provided by the mother alone, is later assumed by 
 the father also, and as the succession of maturing young prolongs 
 the period of conjugal association, with its incidental fostering 
 of family sympathy and feelings of attachment, the family 
 is born, its elaboration giving rise to social as contrasted with 
 merely gregarious relationships. Thus the omission in Darwin's 
 account of the descent of man is made good, as Fiske believed, 
 and the helpless babe is shown to be the instrument of man's 
 peculiarly social and humane endowment. 
 
 Fiske's later statements added little to the original one, but 
 other students have illustrated and elaborated certain features of 
 the theory, while certain contributions must be regarded as posi- 
 tive additions to it. The American naturalist, Marsh, had found 
 from a study of fossil remains evidence of a marked increase in 
 cerebral substance in recent mammals as compared with their re- 
 latives of the lower tertiary epochs. Eocene brains were small, 
 hardly larger than those of the reptiles in some cases. There was 
 a gradual increase in the size of the mammalian brain through the 
 tertiary period, generally in the cerebral hemispheres. The same 
 law holds good for birds and reptiles from the Jurassic to the 
 present. The brain of a vigorous progressing race was relatively 
 large, that of a declining race relatively small. The brain 
 size of young was found to be proportionately greater than that 
 of adult. This brain increase was regarded by Marsh as an 
 important element in survival. 6 
 
 'Amer. Journ. of Sci., Vol. VIII, 1874; abstract in Nature, Vol. XXXII, p. 562. 
 
Human Infancy and the Recapitulation Theory 67 
 
 Lankester regards the conclusions of Marsh as illustrating a 
 general truth, to which the case of Homo and his pithecoid rela- 
 tions is no exception. This authority further considers this 
 progression to be one from action based on instinct to action 
 based on " educability. " Educability is transmitted by heredity 
 but its products are not. Instinct and educability are to a large 
 extent in opposition, the loss of the first making an opportunity 
 for the appearance of the latter. Lewis and Romanes are funda- 
 mentally wrong in imputing instinct to "lapsed intelligence." 
 There is no community between the two. One can grow only 
 as the other diminishes. 7 
 
 In a study of the causes of extinction of mammalia, Osborn 
 assigns to brain capacity, among a variety of causes, a primary 
 importance. The identification of educability with brain size 
 in surviving mammal forms appears clearly in the following: 
 
 " . . . the chief advantages of brain capacity are un- 
 doubtedly in relation to adaptability of habit, resourcefulness in 
 times of exposure, alertness in avoiding new dangers to which 
 the young may be exposed, enterprise in seeking new habitat 
 ." 8 
 
 The early insistence upon the cruelty of the natural order as 
 described by Darwinism, and especially the conflict between the 
 state of nature and that of art and humanity, so vigorously 
 urged by Huxley in his "Evolution and Ethics," brought out a 
 series of replies calling attention to the facts of parental care and 
 mutual aid among animals and men. These facts had been 
 alluded to by naturalists incidentally but were made the principal 
 theme of two very widely read authors. These were Henry 
 Drummond in the "Ascent of Man" (1894) and P. Kropotkin 
 in a series of articles 9 in which the facts illustrative of co-opera- 
 tion among animal and savage societies were brought together. 
 
 In 1898, Sutherland, in the early chapters of the "Origin and 
 Growth of the Moral Instinct," summarized the facts of parental 
 care among the principal vertebrate groups in terms indicative 
 of its historical evolution. The high fertility, rapid hatching, 
 and early maturity by means of which the species of the lower 
 groups were maintained is shown to yield to the biologically 
 
 ' Nature, Vol. LXI, 1900, p. 624. 
 
 • Amer. Naturalist, Vol. XL, 1906, p. 857. 
 
 » Reprinted in Mutual Aid as a Factor in Evolution, 1902. 
 
68 The Recapitulation Theory and Human Infancy 
 
 more advantageous plan, incidental with the lower groups but 
 characteristic of the higher, in which parental care in some form 
 is involved. In its early organic and unconscious expressions 
 parental care was manifested in the safeguarding of germ-cells 
 in the coming together of the sexes. Subsequently the hatching 
 eggs were variously and increasingly protected, notably in the 
 brooding of birds and in the placental gestation of mammals. 
 The extension of parental care to the post-natal period opened 
 the way to the evolution of conscious parental solicitude, gradu- 
 ally increasing in duration and inteDsity. The breeding rate 
 is found to vary with the increasing scope and degree of care 
 from parents. The decrease in the number of eggs and young 
 is associated with a higher nervous organization expressing itself 
 especially in intelligence, and helplessness is made concomitant 
 with intelligence as its necessary condition. 
 
 The peculiar utility of parental care, according to Sutherland, 
 consisted in providing an opportunity for variation in the direction 
 of increasing intelligence. Intelligence in any large amount is nec- 
 essarily associated with delay in the assumption of life-saving abili- 
 ties. Among those animals without parental care variations favoring 
 intelligence, with its coincident delay of maturity, would have been 
 immediately rendered futile by the extinction of the immature 
 animal. There were therefore strict limits to any extension of 
 intelligence among the lower groups. It would increase only to a 
 degree not inconsistent with an independent struggle for existence. 
 With the coming of parental care the way was cleared for an 
 indefinite amount of variation in the direction of intelligence, 
 and thus it is that intelligence is peculiarly the possession of the 
 higher mammals. 
 
 All these contributions to the discussion of infancy and paren- 
 tal care showed clearly that infancy and biological superiority 
 are causally related without indicating just how the associated 
 plasticity of the nervous system was used to bring the improved 
 adaptation about. This last has been done by the psychologists. 
 In connection with his studies upon young animals, reported es- 
 pecially in "Habit and Instinct" (1896), Lloyd Morgan demon- 
 strated with considerable particularity how the imperfect instincts 
 with which the young of learning animals come into the world 
 are adapted to the peculiar circumstances of their existence by the 
 
Human Infancy and the Recapitulation Theory 69 
 
 supplementations of habit. In the view of Morgan intelligence 
 has two functions, that of setting up an equipment of specialized 
 habits during immaturity, and that of the readjustment of these 
 habits in some degree in maturity. "It is in the period of youth- 
 ful plasticity that intelligence has its most important part to 
 play so far as the genesis of habit is concerned." 10 Some intel- 
 ligence remains over for adult life; the higher the mental grade 
 and the more varied the conditions, the greater is the balance 
 left over. But habit formation is peculiarly the affair of infancy. 
 
 Another significant idea from this writer, taken in turn from 
 Hudson's "Naturalist in La Plata," as Morgan acknowledges, 
 is that of tradition, or the transmission by imitation from one 
 generation to another of successful acquired modes of behavior. 
 This fact of imitation has been greatly emphasized in human 
 society since by Tarde, 11 Baldwin, 12 Royce, 13 and Sumner. 14 
 
 Imitation and tradition are to be regarded as two sides of the 
 same fact, the one standing for the process by which the other 
 is brought about. More recent study of animal behavior has 
 tended to minimize the amount of imitation among animals in 
 general, but its presence among the primates is admitted, and 
 in the human species imitation and tradition are so impressive 
 as to be considered by some authorities the most significant of 
 all the factors of its life. It would follow logically, although 
 confirmation from a sufficient knowledge of the life of the higher 
 primates is still lacking, that in the evolution of man and espe- 
 cially in the progression from the ape-like to the human condi- 
 tion, biological well-being and success were closely identified 
 with the transmission of socially derived habits or tradition, 
 in connection with neuro-muscular plasticity. Nature's method 
 of guaranteeing this transmission was through the invention of 
 the instinct or impulse of imitation, a special device, according 
 to Groos, by which modes of action not resting upon well-defined 
 instinctive tendencies could be taken up by the young wholesale, 
 so to speak. There seems to be no other way of adequately ac- 
 
 " p. 157. 
 
 « Laws of Imitation, 2nd. ed. trans., 1902. 
 
 " Mental Development in the Child and the Race, 1895. 
 
 " Outlines of Psychology, 1903. 
 
 « Folkways, 1907. 
 
70 The Recapitulation Theory and Human Infancy 
 
 counting for so profound a disposition as the imitative tendency 
 in the human animal. 15 
 
 In the course of the discussion of imitation the term has been 
 found too inclusive, and there is a noticeable tendency among 
 psychologists to distinguish between instinctive imitation or 
 suggestion and true imitation based upon "copies" existing in 
 terms of related "objects." Suggestion has now an important 
 literature of its own, and while much of it has made slight refer- 
 ence to biological history and any relation to infancy, enough has 
 been said in these connections to make of it a somewhat distinct 
 factor in the transmission of social modes. Suggestion is differ- 
 entiated from imitation in that its excitants are simpler, sensory 
 rather than perceptive and relational. It is therefore found 
 among gregarious animals before true imitation and is illustrated 
 in the pseudo-imitation of schools of fish, flocks of birds, sheep, 
 etc. But it has been retained in human evolution in great force 
 and must be accorded high if not supreme importance in the 
 transmission of social habit. Its primacy over true imitation 
 can scarcely be denied when one considers the comparatively 
 advanced nature of the latter, and its controlling power among 
 primitive and less cultivated men. 
 
 Suggestion and imitation have been intimately associated 
 with play, the biological value of which has been authoritatively 
 shown by Karl Groos. With Groos "the very existence of 
 youth is due in part to the necessity of play; the animal does not 
 play because he is young, he has a period of youth because he 
 must play." 16 Whether or not one should quite agree to the 
 form of this statement, there can be no question of the most 
 intimate relationship of play to infancy. Infancy is the period 
 during which the young animal reaches the adult level of effi- 
 ciency upon which the species is maintained in its struggle for 
 
 Is For the purposes of the present account imitation is referred as to a single or uni- 
 tary thing whereas the term of course denotes a highly intricate complex. In the mind 
 of the writer much confusion in the use of the term is due to an unjust distinction of it 
 from trial and error. Imitation is through and through a trial and error process, but 
 this trial and error is incited by, and in its higher forms in part guided by, the behavior 
 of others. The original or instinctive phase lies in the incitement to some response. This 
 response may be comparatively general to begin with but it becomes more definite by 
 trial and error with its resulting special habits. It is precisely in this combination of 
 instinctive incitement and capacity for adapted and suitable behavior that its biological 
 utility consists. For a specific instinctive response to the behavior of others would 
 prevent the adjustment that imitation obviously provides for. 
 
 h Play of Animals, trans. 1898, preface, p. xx, and p. 75. 
 
Human Infancy and the Recapitulation Theory 71 
 
 survival. This degree of efficiency involves some practice in 
 all learning animals and in many a long continuation of it. 
 This indispensable practice would be fatal if left to the period 
 of independence. It might conceivably have been enforced by 
 parents, as it is to a very slight extent among animals, but this 
 implies a degree of intelligence and foresight beyond the capacity 
 of animal parents, indeed not easily assumed by civilized human 
 parents with all their higher resources. Self-imposed practice, 
 or play, was therefore the simplest biological expedient. If 
 the formula of Groos be understood to assert that infancy without 
 play is useless, its truth must be admitted, and it is fair to assume 
 that infancy and play evolved together. A merely docile plastic- 
 ity could scarcely give rise to the habits of maturity. Play is 
 the necessary middle term between plasticity on the one hand 
 and intelligence on the other. 
 
 These several additions to the ideas of Fiske are brought to- 
 gether in Baldwin's "Development and Evolution" (1902), per- 
 haps without explicit reference to their bearing upon a theory of 
 infancy as such. Their interrelations are, however, there shown. 
 The doctrine of "organic selection," also reported in this book, 
 is not without its implications for the present topic. 17 This 
 theory was presented by three writers independently — Osborn, 
 Lloyd Morgan, and Baldwin — and has obtained a fairly general 
 acceptance. Its general effect is to show how plasticity has 
 determined in part the selection of non-plastic or fixed or- 
 ganic characters. It must have been noticed in the reported 
 statements of Fiske that the evolution of both reflex or instinc- 
 tive and intelligent behavior was explained in terms of use- 
 inheritance. This explanation was not inconsistent with the 
 views prevailing at the time Fiske wrote, but has come to be no 
 longer tenable by reason of the change of emphasis since regard- 
 ing the transmission of acquired characteristics. It was inevi- 
 table that plasticity and its effects should be made to accord 
 with the more acceptable doctrine of the germinal origin of 
 variation and mutation. 
 
 Organic selection assumes that although plasticity is physically 
 inherited its resulting habits are not. But these habits, because 
 of their effect in making adaptations more adequate, would 
 
 17 See Appendix B for the original statements with others. 
 
72 The Recapitulation Theory and Human Infancy 
 
 often have life-saving value as such, and would therefore in the 
 long run preserve and select individuals in whom the fixed and 
 physically inherited germinal variations should increase in the 
 direction of better adaptations. Plasticity and its habits would 
 thus blaze the way along which germinal evolution could follow, 
 because the incidence of natural selection would fall first upon 
 habits and only through them upon the physical make-up of the 
 animal. With the rise of tradition the value of this process 
 would increase, so that on higher simian levels and early human 
 levels the selection of hereditary strains was increasingly deter- 
 mined by the character of the social habits directly or indirectly 
 favoring survival and leaving of offspring. Infancy being es- 
 pecially responsible for the assumption of habits, in this manner 
 becomes intimately related to organic evolution to the extent, 
 that the theory of organic selection is true. 
 
 In the light of these later contributions, Fiske's original state- 
 ment of the theory of infancy requires some amplifying. The 
 biological explanation of infancy assumes that with this period 
 is associated species preservation and success, and in the case of 
 man, species dominance. The advantages accruing to species 
 because of infancy reside in the greater adaptability of individu- 
 ally acquired habits over the mechanical behavior of instinct. 
 This is made possible by an elaboration of the central nervous 
 system, especially in the cerebral portions. But the accumula- 
 tion of habits requires time and practice and a degree of ineffi- 
 ciency and dependence corresponding to the difference at any 
 time obtaining between the neuro-muscular condition of the 
 young and that of the adult. Among the higher primates these- 
 habits are in large part socially derived, calling for the psycho- 
 physical adjustments of suggestion and imitation on the part of 
 infancy to insure their transmission. The inefficiency of infancy 
 necessitates counterbalancing parental oversight, and the indis- 
 pensable practice is obtained by imposing upon the young an 
 instinctive need of self-exercise or play. This spontaneous 
 exercise is directed not only upon well-defined tendencies char- 
 acteristic of the adult life of the species in need of perfecting, but 
 also to modes of social action resting slightly upon an instinctive 
 basis and more largely acquired by successive generations in re- 
 sponse to the changing conditions of their lives. Play is there- 
 fore both specific in its forms and broadly imitative and general- 
 
Human Infancy and the Recapitulation Theory 73 
 
 ized. As to its origin, plasticity is characteristic in small degree 
 of animals other than the higher mammals, but mutations in 
 this direction with their coincident delayed maturity were futile 
 until accompanied by the protection of parents. Plasticity is 
 for this reason conspicuous with mammals. In turn the assump- 
 tion of valuable habits had the effect of preserving and selecting 
 germinal mutations in a given direction which would otherwise 
 have been sacrificed. Finally, the vital energy necessary to the 
 production of organic complexity in the higher learning animals 
 was made possible in some part by the saving from a lowered 
 birth-rate due to the increasing parental care and solicitude 
 given to the eggs and the immature young. 18 
 
 Two recent volumes from the pens of accomplished naturalists 
 discuss the infancy and youth of animals in a convenient and 
 exceedingly attractive fashion. 19 In the main these books con- 
 firm the earlier accounts, but with important minor qualifications. 
 The economic value of parental care as a substitute for great 
 fertility in biological competition is accepted and illustrated by 
 both writers. Pycraft, however, refers to "some puzzling facts" 
 and rejects the view which finds in the mortality of young a 
 cause of exaggerated fertility. Rather, it should be said, fertility 
 encourages mortality by offering large numbers of young for food. 
 Fertility, like extravagance in ornament and gorgeousness of 
 color, is to be regarded as a specific character and not a direct 
 response to biological necessity. Moreover, the relation of 
 fertility to mortality can often be only surmised, from ignorance 
 of the actual natural conditions surrounding many species. It 
 still does not appear that Pycraft's position need be in essential 
 contradiction to the older way of stating the matter, which 
 perhaps failed to clearly affirm that the only effect of selection 
 was the limitation or survival or inherent specific characters. 
 There seems to be small reason for doubting the broad correlation 
 of decreasing fertility and degree of parental care in relation to 
 
 M The following extract from Washburn's Animal Mind, 1908, p. 284, should be 
 reported in this general connection: " One of the most vital meanings of the long period 
 of helplessness and dependence constituting human infancy lies in the fact that by 
 relieving from the necessity of attending exclusively to external objects, it renders 
 possible attention to the sensations resulting from movement; and thus, by supplying 
 an essential condition for the revival of such sensations in idea, it opens the way for 
 the control of movement through the movement idea." The extract should be read 
 with its context. 
 
 " Mitchell, The Childhood of Animals, 1912. Pycraft, The Infancy of Animals, 1913. 
 
74 The Recapitulation Theory and Human Infancy 
 
 mortality, provided it be understood that natural selection need 
 not always have produced an exact or refined adaptation. 
 
 The value of parental care as a necessary condition to the emer- 
 gence of organisms of the higher types and the correspondence 
 of youthfulness with this higher organization is also acknowl- 
 edged by both writers. The greater capacity of the higher ani- 
 mals with the prolonged infancy period is due to a more or less 
 extensive education to fit them for the strenuous activities of 
 their life. This education varies with the different groups 
 and conforms to the necessities of circumstances and the mode 
 of living. To play is attributed a large importance in the prose- 
 cution of this education, and it is interesting to note that on the 
 mooted question as to whether young animals learn directly 
 from their parents both authorities speak with certainty in the 
 affirmative. Mitchell's description of imitation below the mon- 
 keys is, however, a carefully guarded one, and amounts to scarcely 
 more than a belief in organic predispositions to trial and error 
 modes of action which are in some degree encouraged and facili- 
 tated by the presence of similar action on the part of others. 
 With the apes this author holds for something akin to human 
 types of conscious imitation. 
 
 In view of prevailing assumptions regarding the causes of the 
 duration of youth Mitchell's statement in this connection may 
 serve to call attention to the complexity of the facts and yet to 
 show the degree of truth in the assumed parallel between youth- 
 fulness and intelligence in the species. 
 
 "The duration of youth in all [vertebrates] is settled by no 
 invariable chain of organic necessity. It has no relation to the 
 duration of the complete cycle of life from birth to death. It is 
 linked with size, but only in an indirect fashion, most apparent 
 in animals most akin. It is linked much more closely with 
 complexity of organization, so that the higher forms usually 
 take longer to mature than their near but lower relations. It is 
 linked most closely with intelligence, the more intelligent ani- 
 mals having relatively longer youth. And as we pass down- 
 wards from intelligence to instinct we find that the duration of 
 youth shortens." 20 
 
 Helplessness in young animals has been very generally identi- 
 fied with the immaturity of neuro-muscular co-ordinations con- 
 
 " Mitchell, The Childhood of Animals, p. 54. 
 
Human Infancy and the Recapitulation Theory 75 
 
 stitutive of intelligent or adaptive behavior. It appears from 
 the two accounts now under discussion that other causes may 
 contribute to this condition. The young of many carnivores 
 are thought to be born in their imperfect physical state be- 
 cause the agility required of the mother in catching living prey 
 would be seriously hindered by carrying heavy young. Among 
 nestlings in the less precocious birds helplessness is alleged as a 
 safeguard to premature hazardous beginnings in locomotion. 
 Thus helplessness as a condition due to unlearned adaptive 
 powers is to be distinguished from that induced by other biological 
 needs, as well as from that which may be unrelated to any utility. 
 The helplessness which associates with neuro-muscular plasticity 
 is presumably not a general condition at all, but is relative to 
 the learning that any species may accomplish in those special 
 directions characteristic of it. 
 
 With regard to recapitulation in the period of infancy Mitchell's 
 statement is as follows: 
 
 "... the young of nearly allied animals are much more 
 alike than are the adults. . . . We explain this by sup- 
 posing that the evolution of the individual to a certain extent 
 repeats the evolution of the race. . . . We have to re- 
 member, however, that this explanation is not complete, and we 
 shall find many characters of young animals to which it does 
 not apply. The young animal owes its characters not merely 
 to its ancestry; as much as the adult, it has to be fitted to the 
 special environment in which it lives. It is not merely a stage 
 in development, but an independent living creature with its 
 own needs and its own aptitudes, presenting characters that are 
 neither a memory nor an anticipation, neither a relic of the 
 past nor a preparation for the future, but suitable for its own 
 purposes." 21 
 
 The tenor of Pycraft's statement is not greatly different : 
 
 "Time was when it was believed that these early-growth 
 stages, if carefully followed, would reveal all the mysteries of 
 evolution, since, it was supposed, every animal had to climb its 
 own genealogical tree, so to speak. But it was soon found that 
 such hopes were over-sanguine, for records of some of the most 
 important phases have been lost completely, and others blurred; 
 while some of the phenomena have nothing to do with ancestry, 
 
 « Mitchell, The Childhood of Animals, p. 7. 
 
76 The Recapitulation Theory and Human Infancy 
 
 but represent what we may call scaffolding — features which 
 have been introduced solely for the benefit of the individual. 
 The study of young mammals does, nevertheless, throw a 
 flood of light bearing on their ancestry. . . ,' m 
 
 It must be noted that both writers, by the terms infancy 
 and youth, refer not only to that period of plasticity in the early 
 life of animals of the learning type, but to the period following 
 hatching whether plastic, larval, or merely precocious and essen- 
 tially unmodifiable, as with growing reptiles. If we limit the 
 application of their remarks to the period of plastic neuro-mus- 
 cular development, certain other statements of these authors 
 should be considered. Mitchell, for instance, with reference 
 to the mammals, the group in which the period of plastic infancy 
 is most conspicuous, writes as follows: 
 
 "Mammals, when they are born or very soon afterwards, 
 closely resemble their parents. The differences are due to 
 greater likeness to ancestors and to their nearest allies, to the 
 absence of special weapons or ornaments, or to the presence of 
 characters useful to the young themselves." 23 
 
 One gathers that the period of youth among mammals is not 
 essentially recapitulatory but rather adaptive and anticipatory. 
 Nevertheless, both these authors present a very considerable 
 number of youthful characteristics which they explain as re- 
 tained ancestral features. From the account of Pycraft are to 
 be noted the following: certain cases of "milk-teeth"; horns of 
 ruminants; antlers of deer; the presence of a hairy covering 
 which does not persist; the under-fur of one group of seals; 
 spines in certain Insectivora; and the familiar ape-like features 
 of the human infant. Pycraft concludes his list with the remark, 
 "We might add considerably to the number of instances of this 
 kind." 
 
 In the matter of coloration the case is complicated and some 
 difference of opinion is expressed, yet the two authors agree in 
 the statement that the young of mammals very commonly 
 show differences in coloration when compared with adults, the 
 youthful coloration being regarded by both as older, the adult 
 as a later modification. 
 
 » Mitchell, The Childhood of Animals, p. 40. 
 *> Op. cit., p. 13. 
 
Human Infancy and the Recapitulation Theory 77 
 
 Thus the youth of mammals is not devoid of ancestral features. 
 These may be "recapitulatory" either because they resemble 
 features of the youthful period of the ancestor, or because they 
 represent the actual adult ancestral condition modified in descent. 
 It would be a matter for study in each case. Still, this does 
 not make youth essentially recapitulatory, for these features 
 are comparatively few when measured against the total make- 
 up of the young animal. They exist alongside others which 
 are adapted to the infantile condition as such, and in spite of 
 what is declared to be a close resemblance of young and adult 
 mammals, taking the group as a whole. 
 
 3. Recapitulation and Human Infancy. 
 
 Before undertaking a discussion of the relation of the theory 
 of recapitulation to human infancy — more especially to the mental 
 traits of infancy — it will be well to consider just what may be 
 properly understood by ancestral reference in this connection. 
 It is obvious, in the first place, that there is nothing to correspond 
 to palaeontological evidence, the court of last resort on the physi- 
 cal side, — unless something of value may be inferred from the 
 structure of fossil skulls. Ancestral allusions to racial mind 
 must be made in the main to what can be inferred legitimately 
 from objective behavior in the scale of living animals, and 
 since these animals are almost universally end-forms in a long 
 process of specialization away from common ancestors, it is 
 clear that inferences as to phyletic mentality are extremely 
 hazardous. If, however, a mental or physical trait peculiar 
 to infancy has a fairly well-defined homolog among lower animals 
 that may be regarded as closely related to probable ancestors, 
 there is ground for assuming an ancestral reference. If the case 
 is one of degree, there must be reasonable certainty of a greater 
 resemblance to the ancestral homolog than to the infant's own 
 adult condition. There will be no justification for assuming 
 an ancestral reference simply because an infantile trait shows 
 some analogy to any animal trait whatever, and surely none 
 merely because no prospective, adult, or adaptive reference 
 can be made. Biological utility is no longer a category of uni- 
 versal application. Heredity is now known to carry much more 
 than the materials of organic adaptations, having laws of its 
 
78 The Recapitulation Theory and Human Infancy 
 
 own which operate without reference to such adaptations. 24 
 Unfortunately a very considerable number of the examples 
 offered for recapitulation in infancy are merely fanciful or even 
 wholly absurd because of a neglect of these obvious logical require- 
 ments. Unless these limitations are acknowledged the ancestral 
 doctrine of childhood becomes meaningless. For if by recapitula- 
 tion or ancestral reference is meant only that the organized and un- 
 acquired part of the mind is due to its history, without regard 
 to a disparity in kind or degree as between infancy and maturity, 
 this is simply equivalent to declaring that the hereditary part 
 of the human mind is inherited, a statement of little descriptive 
 value. That the recapitulationist has done good service in 
 emphasizing the racial character of mind, whether adult or youth- 
 ful, is not questioned. The point at issue is whether infancy is 
 peculiarly ancestral, that is, older than maturity. 
 
 A faithful application of the traditional idea of recapitulation 
 to psycho-physical behavior would mean that as the individual 
 develops it will rehearse in a chronological way the chief stages 
 of psycho-physical evolution in the phylogeny, except as this 
 has been disarranged by direct or cenogenic modifications. 
 There rests upon the advocate of this view, then, the necessity 
 of showing that the sequence of developmental stages is really 
 representative of the racial sequence, and that the constituent 
 phases in the progression are truly homologous with the ancient 
 stages and not merely analogous or convergent phenomena. 
 
 This consistent application of the biological theory has rarely 
 been made to infancy and mental genesis. Recapitulation has 
 taken the form, for instance, of the declaration that the psycho- 
 physical functions appear in the individual in the order of their 
 racial evolution. So stated the doctrine disregards the repre- 
 sentativeness in development of the whole phylogeny. All 
 existing functions may be comparatively recent and many, or 
 even most of them, may have been lost. Those that do appear, 
 however, rise in the phylogenetic order. This view of psycho- 
 physical recapitulation varies from that derived from embryology 
 in another particular, for whereas biological recapitulation 
 assumes that the individual passes through and leaves behind, or 
 radically makes over, its recapitulatory stages in the progression 
 
 « See Bateson, Problems In Genetics, 1913. 
 
Human Infancy and the Recapitulation Theory 79 
 
 towards the specific adult form, the view in question has refer- 
 ence merely to the appearance of psycho-physical features, which 
 thereafter remain functional for life; for example, in the statement 
 that the emotions appear in the order of their rise in the race. 
 
 From these more or less direct applications of the biological 
 theory there is noticeable a grading off to a less and less chrono- 
 logical notion of it, as there is in embryology, until recapitulation 
 is supposed to be illustrated in any juvenile retention of ancestral 
 adult characteristics, or indeed of any ancestral traits whatever, 
 juvenile or adult. 
 
 However these interpretations of recapitulation may differ, 
 they have in common the idea that infancy is essentially retro- 
 spective, rather than adaptive and preparatory. This idea 
 therefore becomes the chief point of attack in any criticism of 
 the theory of recapitulation in its psycho-physical applications. 
 
 There is perhaps little profit in attempting to assign to specific 
 writers the different interpretations of psycho-physical recapitu- 
 lation just alluded to. These have not been clearly distinguished 
 in the literature of psycho-genesis, and since the guiding ideas 
 were so directly taken from embryology the history of the dis- 
 cussion there is the really important matter. 
 
 Romanes seems to have been the first to undertake along 
 inductive lines a detailed comparison of human psycho-genesis 
 with the history of mind as exemplified in existing animals. 
 A glance at the diagram at the beginning of " Mental Evolution 
 in Animals" (1885) will reveal the results of his effort. A glance 
 will suffice also to show its essentially artificial character. The 
 comparison was extended with greater thoroughness in " Mental 
 Evolution in Man" (1889). To the mind of Romanes the dia- 
 gram indicates "in how strikingly quantitative, as well as quali- 
 tative, a manner the development of an individual human mind 
 follows the order of mental evolution in the animal kingdom." 26 
 
 As is well known, President G. Stanley Hall has had a large 
 part in the extension of the doctrine into the field of infancy 
 and mental genesis, and it is not surprising that his "Adoles- 
 cence" (1904) should assume it throughout. Hall's statements 
 are made with the full admission of cenogenic "distortion," 
 "confusion," etc.; but the underlying adherence to the chrono- 
 
 " Mental Evolution in Man, p. 5. 
 
80 The Recapitulation Theory and Human Infancy 
 
 logical conception is unmistakable. One allusion among many- 
 is the familiar one to the period of childhood from nine to eleven 
 years as representing "a terminal stage in human development 
 at some post-simian point." This period is followed by adoles- 
 cence "which recapitulates the long pilgrimage of the soul from 
 its old level to a higher maturity which must have taken place 
 in the race in certain of its important lines long before the his- 
 torical period." 26 
 
 Statements of the kind are legion. 27 Two others will serve 
 the present purpose. One is from the biologist Tyler, who says, 
 "The child is naturally successively animal, anthropoid, half- 
 barbarian, and then civilized." 28 The other is taken from the 
 literature of the "boy problem" which is fairly saturated with 
 the doctrine. "We are by turns vertebrates, gill-breathing 
 vertebrates, lung-breathing vertebrates (we make the great 
 change at birth), little monkeys, little savages, and finally 
 civilized men and women." 29 
 
 It now becomes our object to examine briefly the facts of 
 human infantile recapitulation. It will be impossible to cite 
 every allusion of the kind, for these have been made casually 
 in the course of numerous papers on an indefinite number of 
 topics. The present intention is limited to a general charac- 
 terization of classes of cases and to probabilities in the light of 
 accepted principles of general genetic psychology. The degree 
 of ignorance still prevailing with respect to the course of individu- 
 al and racial psycho-genesis prohibits more than a preliminary 
 survey of the topic. 
 
 In making this survey of the facts we have the advantage of 
 an hypothesis derived from the revision of the biological attitude 
 toward the ancestral facts of embryology, as summarized in the 
 preceding chapter, and illustrated further in the section on 
 human embryogeny. What is true of embryogeny may be true 
 of infancy. We may keep in mind the idea that the ancestral 
 life-history has been transmitted from generation to generation 
 as a whole, and that it has been altered with each step in descent 
 rather than extended. In keeping with this view infancy prob- 
 
 "Vol. II, p. 73. 
 
 " See Thomdike, Original Nature of Man, 1913, pp. 249-252, for an interesting collec- 
 tion. 
 
 28 Growth and Education, 1907, p. 53. 
 
 a Puffer, The Boy and his Gang, 1912, p. 77. 
 
Human Infancy and the Recapitulation Theory 81 
 
 ably has had its own evolution, having been evolved when it 
 was needed, and having been altered from age to age from germi- 
 nal mutation, and by selection as the necessities of its circumstan- 
 ces required. We should expect to find in infancy a compara- 
 tively small number of traits having an ancestral reference merely. 
 These traits would be scattered and not related in a chronolog- 
 ical sequence suggestive of phyletic recapitulation, and their 
 ancestral reference would be first to ancestral infancies and only 
 indirectly to adult characters for which the infantile condition 
 was preparing. Some ancestral traits would perhaps have been 
 made over in part to meet new conditions, and there would 
 likely be an insignificant number of useless rudiments. 
 
 The most important group of facts adduced in favor of mental 
 recapitulation are those referring to a savage human condition, 
 as illustrated in the behavior of lower living races of men. 30 
 These include a large number of instinctive tendencies, especially 
 among boys, which are characteristically savage. Some of these 
 are the love of games embodying running, dodging, throwing, 
 hitting with a club, wrestling, boxing; a strong interest in ad- 
 venturous undertakings, fishing, swimming, exploits requiring 
 endurance, courage, self-control, daring; outdoor interests in row- 
 ing, sailing, climbing, exploring, the handling of animals, hunt- 
 ing; the instinctive grouping in "gangs," group undertakings, 
 hero-worship, group loyalty, antipathy for outsiders, fighting, 
 with all its savage excesses, predatory excursions. The facts 
 are too familiar to require further illustration. 
 
 But this whole group of cases cannot be regarded as ancestral 
 or in any sense recapitulatory; in fact it points quite the other 
 way. The living races of men, to whose modes of life these 
 examples all refer, belong to one species. The older view of 
 Spencer, Galton, Fiske, and others, which held for an organic 
 difference between savage and civilized human nature, has 
 been supplanted by a conception of the essential identity in the 
 hereditary make-up of all races regardless of the degree of civili- 
 zation. 81 
 
 The differences between civilized and savage men are chiefly, 
 if not wholly, acquired and are due to the unlike exploitation of 
 
 » See Chamberlain, The Child, Chap. VIII, and Swift, Mind in the Making, Chap. 
 II, for convenient summaries. 
 
 a See Boas, Mind of Primitive Man; also, Thomas, Source Book for Social Origins. 
 Part II, and bibliographies. 
 
82 The Recapitulation Theory and Human Infancy 
 
 human capacity by traditional and environmental forces. The 
 savage character of boyhood is thus shown to be a necessary 
 preparatory adaptation to the adult conditions prevailing at 
 the period when human nature had assumed its specific form, 
 conditions which are roughly pictured in the instinctive equip- 
 ment of the boy whether the circumstances of his later life are 
 still fairly true to the ancient pattern in some contemporaneous 
 savage society, or whether they have been radically modified 
 in the course of historical development. If this kind of boyhood 
 in some respects seems out of place in civilization, it is not because 
 it is rehearsing a former ancestral adult condition of life; it is 
 due to the fact that the traditional and socially acquired habits 
 have altered so much for the adult in some societies that what 
 the boy is by nature disposed to do is not, superficially at least, 
 just what is expected of him as an adult in these societies. Civili- 
 zation has affected boys and adults probably equally. If this 
 should not be admitted, and a greater resemblance be found 
 among the young in different culture levels, this could very well 
 be accounted for by the fact that the inhibition, selection, and 
 organizing of the inborn qualities by habit and intelligence, 
 have had less time to register their differentiating effects. 
 
 This last thought may be used to explain another class of 
 facts which has been supposed to illustrate recapitulation. 
 Children are thought to betray ancestral limitations in their 
 primitive tastes, their love of myth and of melodrama, of crude 
 music, dancing, the spectacular, strong colors, etc., and on the 
 side of conduct, in their laziness, desultoriness, dislike of work, 
 discontinuity of attention, stealing, lying, truancy, teasing and 
 bullying. But these things are not peculiar to children; they 
 are found equally among uncultivated adults in civilized and 
 uncivilized societies, and merely record the lack of cultural and 
 moral discipline and the coercion of civilized industry. They 
 manifest themselves wherever civilization is lacking, as in isolated 
 or unfortunate classes in modern life, or in tramps or delinquents 
 who for some reason have escaped its influence, and they are 
 not unknown in cultivated adults when the tension of civilized 
 habit is temporarily or suddenly removed. 
 
 |i Continuing the process of elimination, we may refer to one 
 other group of alleged recapitulatory facts. This includes cer- 
 tain emotional attitudes associated with objects acting as their 
 
Human Infancy and the Recapitulation Theory 83 
 
 excitants. These may be illustrated by the fear of snakes and 
 other animals, of celestial objects, of fire, darkness, eyes, teeth, 
 solitude, death, disease, ghosts, etc. A very large number of 
 similar attitudes have been cited as evidence of the recurrence 
 in childhood of ancient attitudes which have been inherited. 
 In all these cases there is evident a confusion of the inherited 
 and the acquired. We are indebted to McDougall's " Introduc- 
 tion to Social Psychology" (1908) for a lucid explanation of 
 this matter. Each of the basic instinct-emotions has its charac- 
 teristic "native excitants," with the inherent power of rendering 
 it vital, or setting it up in psycho-physical behavior. Sensory 
 abruptness, especially of sound, has this effect with fear; inter- 
 ruption of normal functions is a similar excitant for anger; as is 
 the infant wail for parental solicitude. The various native 
 excitants have not as yet been satisfactorily described but the 
 general principle seems clear enough. It follows that certain 
 "objects" or acquired units of perception built around these 
 excitants, will often have an emotion-exciting value because they 
 so vividly contain the native excitants; such objects are thunder 
 for fear or substances of vile odor for disgust. Other objects 
 will have these emotion-exciting effects by association with 
 the original ones, and it is apparent from the observed variety 
 of these derived or acquired excitants that there is scarcely any 
 limit to their multiplication. Almost every aspect of the natural 
 world has been such a fear excitant, if we may believe the ethnol- 
 ogists, and there is probably no conceivable object which may 
 not have this function under appropriate suggestion. Only 
 native excitants, then, can have ancestral reference, and we may 
 safely neglect all objects connected with emotional attitudes and 
 confine our attention to the possible recapitulatory value of 
 excitants as such. 
 
 Undoubtedly native excitants are very old, but as common 
 experience testifies, they are not peculiar to infancy, and they 
 cannot therefore be regarded as recapitulatory in this sense. 
 It is not impossible that such native excitants may become so 
 embedded in complexes with more dominant emotion-exciting 
 excitants as to lose their original force. Such may be the case 
 with aesthetic or religious objects containing essentially ugly 
 or even essentially disgusting elements, but this does not of it- 
 self assign the native excitant to infancy because it works there 
 
84 The Recapitulation Theory and Human Infancy 
 
 in simpler fashion. As to the excitants of attention, curiosity, 
 and their derivative "interests," it is probable that the more 
 conspicuous of these (such as sensory intensity, massiveness, 
 visible motion), are common to children and adults. The 
 strange-in-the-f amiliar as an incitement to attention and thought 
 apparently affects both alike. Much of the "peculiarity" 
 assigned to children's interest in natural phenomena and in 
 the images of their minds can with practical certainty be assigned 
 to the unlikeness in apperceiving content due to intellectual 
 immaturity. The incitements to activity seem very closely 
 related to children's capacities; when they find they are able to 
 grasp they are interested in grasping, when they discover they 
 can walk or climb, they take to these things with avidity, and so 
 on through the succession of childish, youthful, and adolescent 
 "activities." In these things childhood and youth are very 
 obviously preparatory. Excitants are here nicely adjusted to 
 disposing the young animal to undertake his own education the 
 moment the underlying structures are ready. 
 
 It is generally assumed that instinct represents the ancient 
 basic structure upon which plasticity has supervened. A natural 
 inference would identify the native excitant as the original cue 
 to the unmodifiable action which preceded the plastic or habit- 
 induced action in the phylogeny. This is of course not necessari- 
 ly the case, for the original cue may have altered in descent along 
 with the supervening plasticity, in accordance with the theory of 
 organic selection. However, it is at least likely that the native 
 excitant is a conservative and comparatively ancient feature 
 of psycho-physical organization, even if it has not remained 
 wholly unchanged. If this is so, the progression in the infant 
 from the native excitant to the "meaning" which absorbs it, is- 
 homologous with the original phyletic progression from the 
 ancient sensori-motor to the percept-motor action system, and 
 we are apparently confronted with a genuine case of ontogenetic 
 rehearsal or "recapitulation." 
 
 If now we turn to the motor aspect of the presumably ancient 
 instinctive structure we find the distinction, commonly assumed, 
 between its inherited and involuntary expressions and the ac- 
 quired habits which grow up with use and exercise. But the case 
 here is not the same as with excitants and meanings. Plasticity 
 presumably has not been merely added to instinctive muscular 
 
Human Infancy and the Recapitulation Theory 85 
 
 action; it has reduced it, permeated it, and substituted for it; 
 that is, essentially altered it rather than supplemented it. As 
 Lankester puts it, plasticity can rise only as instinct yields it 
 place. It is customary, therefore, to speak of the involuntary 
 instinctive motor expressions, — those discussed by Darwin and 
 other students of the emotions — as remnants of older and more 
 complete action systems. With what degree of justice this 
 assumption is made is a question, for the evolution of skill is a 
 comparatively neglected topic. Students of the animals have 
 thus far been chiefly concerned with the problems relating to 
 animal intelligence. 
 
 Still, there is probably no counterpart to the genetic sequence 
 from native excitant to meaning on the side of motor control. 
 In fact the situation seems just reversed. For phylogenetically 
 there was a progression from stereotyped behavior to less and 
 less fixed modes of behavior. Ontogenetically the progression 
 is from a few established modes to an indefinite number of adapted 
 voluntary habits. And these acquired habits cannot be homol- 
 ogous with the instinctive phylogenetic action systems, for 
 the very good reason that motor plasticity was evolved for the 
 express purpose of substituting better and different action systems 
 for them. 
 
 There is, however, the possibility that there may be examples 
 of recapitulation among the various types of inherited modes of 
 movement: the automatic visceral control, the involuntary 
 accompaniments of the emotions, (fear, joy, grief, "expression"), 
 the random movements of early infancy, and the true reflexes. 
 With respect to the first two, so far as the writer is aware, there 
 are no essential differences between youth and maturity excep- 
 ting such as are induced by habit with the second, and none that 
 requires an ancestral explanation. Mumford" advanced the 
 theory that the random movements of early infancy, associated 
 with the gradual ripening of the lower centers, are reminiscent in 
 certain cases of ancient aquatic modes of action. The suggestion 
 is perhaps a possible one without being at all convincing, and 
 surely the resemblance is not conspicuous. Besides, as Miss 
 Sbinn notes, in commenting on the suggestion, many of the 
 movements such as the asymmetrical movements of the eyes, 
 
 » Brain, Vol. XX, 1897. 
 
86 The Recapitulation Theory and Human Infancy 
 
 grimacing, the rolling of the head, cannot be brought under the 
 theory at all. 33 
 
 The sucking and crying reflexes of the infant are obviously 
 adaptations. As for sneezing, yawning, coughing, and similar 
 reflexes, all these appear early and remain essentially unchanged 
 through life. Certain other reflexes and a number of physical 
 traits, were collected by Robinson, 34 and Buckman, 36 and offered 
 as illustrations of recapitulation. Examples of infantile adaptive 
 characteristics from these writers referring to the pithecoid 
 infantile condition are the clasping reflex, the supporting of the 
 body by the hands and arms, the thumb-like action of the big- 
 toe — all having to do with the necessity of holding fast to the 
 hair of the mother in arboreal life. The very early "hide and 
 seek" propensity of babies is another example of pithecoid 
 recapitulation. Examples of physical traits are the baby's 
 snub nose, prognathism, remnant of lip furrow, tail mark, Jong 
 arms, position of the legs and feet, and the plantar lines. If 
 one should be disposed to grant a certain plausibility to these 
 cases of ancestral reference, there is still no necessity of assigning 
 them to the adult monkey or ape, where they are not obviously 
 infantile. They may very well resemble the adult because of the 
 infant ape's resemblance to its own adult condition and they 
 thus become illustrative of ancestral ontogenetic resemblance. 
 They may be compared with the many pithecoid vestiges remain- 
 ing in the human adult organization, and before any assertion of 
 greater antiquity of infancy as such can be made it is necessary 
 to show that they are representative of a very much larger group 
 of such vestiges than can be found in adults. This is to say, 
 the whole human ontogeny has pithecoid vestiges. Of course 
 infancy has its share. 
 
 Other illustrations of recapitulation from the same source 
 are referred to the conditions of primitive man. The intensity 
 of fear in children, useless crying, shyness, the instinctive appeal 
 and clinging to the parent in the presence of strangers, — these 
 recall the dangers of the early life of man. The greediness and 
 selfishness of children point to a considerable degree of parental 
 neglect and a consequent survival of those who managed to fend 
 
 " Notes on the Development of a Child, Vol. I, p. 397, footnote. 
 " Nineteenth Century, Vol. 30, 1891; Vol. 31, 1892; North Amer. Bee.. Vol. 159, 1894; 
 Brit. Med. Journ., Vol. 2, 1891. 
 " Nineteenth Century, Vol. 36, 1894. 
 
Human Infancy and the Recapitulation Theory 87 
 
 for themselves. The plumpness of babies as a precaution against 
 famine, infantile attractiveness as an evidence of primitive paren- 
 tal selection, the strong interest in animals, the carrying of things 
 to the mouth, and many other childish characteristics are given 
 their appropriate recapitulatory explanation. The value of this 
 type of evidence will doubtless vary with the sense of credulity, 
 but, accepting them at their face value, it is to be noted that 
 some of these traits may still be of value to the species in existing 
 savage societies, others refer to infantile adaptations in the past 
 and not to remote recapitulations, and once more illustrate the 
 familiar principle of ancestral ontogenetic resemblance. Infants 
 today resemble the infancies of their ancestors just as adults 
 today resemble ancestral adults. 
 
 As for emotional equipment, children and youth have no 
 characteristic attitudes of the kind which are inaccessible to the 
 sympathetic appreciation of adults. Like native excitants their 
 early character may be simpler, but they are not different in 
 quality. The one attitude, which by reason of its oddity for 
 adults has been designated a "mania," is that of collecting. 36 
 One has difficulty in seeing a preparatory value in this propensity. 
 Perhaps it had an adaptive value in earlier infancies. Seemingly 
 fear is intensified with young children, and it may be the egoistic 
 sentiments are more powerful relatively throughout the earlier 
 part of immaturity. It has been noticed that Robinson saw 
 in these things illustrations of infantile adaptation. The two 
 great sources of altruism are more especially associated with 
 advanced stages of development, — friendship with the clannish- 
 ness and romantic love of the pubertal and adolescent years, 
 parental regard with the coming of offspring. Childhood, 
 although not devoid of these sentiments, does not need them in 
 the same way. Its major business is to practice its own individual 
 powers. 37 
 
 Drummond, 38 following Romanes, asserted categorically that 
 the order of the appearance of the emotions in growth is the 
 order of their distribution on the scale of animals. As to this 
 
 " Thorndike finds abundant evidence of this instinct among adults, op. cit., p. 267. 
 
 « For a pungent criticism of the recapitulation theory as applied to mental genesis, 
 together with a clear statement of the "utility" theory, of which he is an advocate, 
 see Thorndike, op. ell., chapter XVI. For an earlier statement of this latter theory, see 
 King, Psychology of Child Development, 1904. 
 
 » Ascent of Man, p. 133. 
 
88 The Recapitulation Theory and Human Infancy 
 
 it must be said that the lack of knowledge of the probable facts 
 in either series prohibits inferences. 39 
 
 Grouping together the less propulsive and more passive in- 
 herited psycho-physical traits under the head of "sensibilities," 
 it is to be noted that President Hall and others have called atten- 
 tion to possible recapitulations in this region. Certain hedonic 
 qualities attached to sensations of touch, smell, and taste, 
 especially, are thought to require an ancestral explanation, 
 one reason for this being the probable degeneration of these 
 senses and their old-time greater importance. This is not an 
 unreasonable attitude, for the protection afforded by the evolv- 
 ing higher senses might well permit the carrying down of useless 
 remnants of the kind. Instincts, intelligence, and modes of 
 action under the guidance of sight and hearing, would doubtless 
 be more directly subject to natural selection. There is, however, 
 a lack of convincing evidence of any predominance of such traits 
 with the young as such, and until this is forthcoming there is no 
 need of appealing to recapitulation for an interpretation of such 
 cases as may seem truly vestigial to adults. 
 
 Baldwin's acceptance of recapitulation was due in part to his 
 belief in its unimpaired standing in biology as late as 1906, to 
 the idea that it was logically required as an effect of heredity, 
 and to the parallel he found between the great epochs of psycho- 
 physical evolution in the race and comparable epochs in individual 
 mental development. 4J It is true Baldwin noticed very signi- 
 ficant departures from a faithful psycho-physical recapitulation, 
 some of which have been referred to in the present discussion. 
 Indeed they might well seem to his reader much more impressive 
 than the arguments he adduced in support of the theory. Bald- 
 win's first two reasons for a modified acceptance of recapitula- 
 tion have been sufficiently discussed. Without following his 
 analysis in detail we may consider briefly his empirical support 
 of the theory in terms of current ideas of psycho-physical evolu- 
 tion and development. The students of comparative psychology 
 have agreed fairly well upon the main outlines in the evolution 
 of behavior. The series of epochs in this evolution is represented 
 as follows: The period of the tropisms; that of the reflex and the 
 essentially unmodifiable instinctive behavior; that of very grad- 
 
 «' Compare Thorndike, op. cit., p. 256. 
 
 «o Mental Development, Chap. I. Development and Evolution, Chap. I. 
 
Human Infancy and the Recapitulation Theory 89 
 
 ually modified instinctive behavior; that of intelligence, or the 
 more abrupt adjustment of instinctive modes to the perception 
 of related "objects," with its associated revival and desire; that 
 of the imitative and lower types of conceptual intelligence of the 
 primates; and finally the rational learning of man. 41 These 
 are of course not distinctly marked periods but rather points 
 of emphasis in a gradually changing evolution. To what extent 
 is the series paralleled by the development of the human individ- 
 ual? It is wholly beyond the scope of the present discussion 
 to make a careful study of the correspondence. One can here 
 speak of probabilities only, in view especially of our ignorance of 
 the course of individual development. The underlying organic 
 structures are of course wholly incomparable. They are as 
 unlike as the complicated human nervous system at birth and 
 undifferentiated protoplasm, to refer to the two extremes; or 
 as the infant human and pithecoid brain, to narrow the interval 
 of contrast. The point at issue is whether the rise of psycho- 
 physical functions in the human child follows in an homologous 
 fashion the course marked out by the evolution of behavior. 
 The nervous control of human behavior offers no ground of 
 comparison with the tropisms. With regard to the reflexes of 
 infancy, it is obviously impossible to establish genuine homologies 
 with the lowest animal reflex action systems. In their origin 
 they were undoubtedly removed from primordial phylogenetic 
 systems by inconceivable intervals of time, and their only common 
 attribute is their reflex quality. Moreover, they do not consti- 
 tute an "epoch" in development, in the sense that they are 
 succeeded by a later and different mode or organization, for 
 they persist throughout life. The random movements do sub- 
 side and give way to higher systems, but even if these be regarded 
 as peculiarly ancestral, they are so only as fragments of older 
 more complete instinctive systems and not as representative 
 ancient reflexes. Again, it is not at all obvious that the particu- 
 lar reflexes that remain in man are especially old in comparison 
 with his instinctive make-up. The sucking reflex has risen 
 with the mammals; it is probably much younger than the basic 
 fear structure. What is true of this reflex may be true of others. 
 
 « See Hobhouse, Mind In Evolution, 1901 ; Morgan, Animal Behavior, 2nd. ed. 
 1908; Holmes, The Evolution of Animal Intelligence, 1911. 
 
90 The Recapitulation Theory and Human Infancy 
 
 Similarly the instincts do not constitute an epoch in human 
 development for they also rise early and persist through life, 
 speaking generally. But we have noted that the progression 
 from the native excitant to "meaning" seems to represent a 
 phylogenetic rehearsal, and we are confronted by the very signi- 
 ficant fact that the sequence from assimilative through intelligent 
 to conceptual learning is one that has been illustrated in the 
 accounts of the evolution of intelligence indifferently from the 
 animal series and the course of the child's intellectual progress. 
 Romanes, for instance, believed implicitly in the closest possible 
 correspondence of animal and childish modes of thought, up 
 to the point where human intelligence passes beyond the limit 
 of animal capacity. 42 And this assumption of a fundamental 
 likeness of childish to animal modes of learning is not confined 
 to older accounts but passes as a sort of commonplace in current 
 discussions of intelligence. It has been very generally held 
 since Romanes that the differences in intelligence whether ex- 
 hibited in animals, primitive men, or children are differences not 
 in kind but in degree, and there is undoubtedly implicit in these 
 views the thought that there exists some kind of scale or genetic 
 progression against which all acts of intelligence may be measured. 
 It has, in fact, been assumed, whether properly or not, that 
 intelligence in its representative character cannot differ in kind 
 but only in degree. For intelligence has been regarded as 
 yielding a direct acquaintance with the environing world, so 
 that a better acquaintance with this world could only mean a 
 more adequate relationship of the same kind. If, then, lower 
 animals have any intelligence they must possess some amount 
 of the same thing which higher animals and human beings 
 possess in larger measure. 43 The progressive character of the 
 
 12 Mental Evolution In Man, passim. 
 
 a That its a priori attractiveness has favored this assumption is probably true. 
 An adequate treatment of it in the light of the available facts is beyond the possi- 
 bilities of this account. Yet a few obvious considerations may be noted. The low 
 type of learning involved in the dropping of useless movement or in threading a maze- 
 may be effective without being representative, and so escape the implication of the 
 assumption in question. The possession of a free prehensile organ has been noted as 
 of first importance in the perception of objects and their qualities, and as a probable 
 source of difference between human or pithecoid and lower animal intelligence (com- 
 pare Washburn, Animal Mind, p. 279). And the contribution of the linguistic func- 
 tion to intelligence must be remarked, whatever this is. That much remains to be 
 said for the view here referred to, despite such considerations, is apparent. See, for- 
 instance, Morgan, Animal Behavior, pp. 332 el seq. 
 
Human Infancy and the Recapitulation Theory 91 
 
 evolution of intelligence has derived added support from the 
 views currently held of the historical increase in complication 
 of the nervous system, especially of the cerebral portions. The 
 original segmental nervous system has been successively inte- 
 grated, first by co-ordinating centers of limited scope, and suc- 
 cessively by hierarchies of increasing range and inclusiveness. 
 This evolution has been in the main one of gradual progression 
 in a given direction, and those portions associated with intelli- 
 gence are regarded as being peculiarly illustrative of this order. 
 In a passage in which he characterizes the method of his work 
 on the evolution of mind Hobhouse speaks somewhat explicitly 
 of the homologies existing between human and animal modes 
 of intelligence. Referring to the stages in mental evolution as 
 summarized in Chapter XV of his book, this writer says, 
 
 "The fourfold method of correlation differing stage by stage 
 (a) in respect of the factors explicitly taken into account, and 
 (bj therewith in extent of the sphere comprehended, appears to 
 the writer to be realized in human consciousness as we run the 
 gamut from philosophical reflection down to the quasi-mechan- 
 ical response of habit. Whether these stages into which de- 
 veloped human reason can be analysed correspond to stages by 
 which it grew is of course another question — a question only to 
 be answered by a much wider knowledge of animal psychology 
 and of the distinct processes of human development than we at 
 present possess. If we accept evolution, analogy suggests that 
 human intelligence is a specific and higher development of a 
 more general form of intelligence. Hence, if we cut away the 
 higher development, we should come to something roughly 
 common to man and the higher animals. If we cut further, 
 we should come to something common to man and a wider 
 class of animals, and so forth. But there is a caution to be 
 borne in mind. No two species will come to a quite identical 
 development. No part of the physical structure of man, I 
 suppose, is precisely equivalent to the homologous part in 
 another mammal, still less in another vertebrate of a different 
 class. It is the same with the mental structure. We must not 
 expect to find any animals whose intelligence falls readily into 
 any classification based on the analysis of human experience. 
 We can only expect to find homologous developments. That 
 being understood, it may be said that the method of the preced- 
 ing chapters, so far as they relate to animals, has been to analyze 
 out the phases of intellectual development as distinguishable in 
 human experience, and to discover what homologous structures 
 
92 The Recapitulation Theory and Human Infancy 
 
 are to be found in the animal world. In accordance with these 
 homologies animals are ranked in the classification. 44 
 
 Hobhouse here again gives expression to the pervasive idea 
 that has played so large a part in all ontogenetic study, namely, 
 that the theory of evolution implies a progressive historical 
 sequence that becomes registered in development. We now 
 know that this is not the only method in evolution. Rather, if 
 the evidence presented in the first chapter is representative, it 
 is the unusual one, the life history being so altered in the suc- 
 cessive stages in descent as to leave comparatively few evidences 
 in any one ontogeny of what took place in the phylogeny. But 
 it may be that in the case of intelligence there has been just 
 such a progression. The theoretical considerations to which 
 reference has just been made, and the degree of success which 
 has attended the work of students of mental evolution who have 
 assumed it, give a fair presumption of its actuality. The prin- 
 ciple of homologous relationships obtaining between animal 
 and childish modes of thought therefore remains as a valid 
 working hypothesis, and recapitulation may reasonably be ex- 
 pected to find illustration in this direction. What we already 
 know of the correspondence, however, forbids the acceptance of 
 Romanes' belief in a close similarity. It may be, for instance, 
 that the phylogenetic order is not so much shown through 
 chronological periods of immaturity as in the progression from 
 ignorance to conceptual or rational control at any period of 
 growth. And there is the further possibility that intelligence 
 has been adapted not only to human interests as contrasted 
 with animal interests — which is obviously the case — but to par- 
 ticular phases of psycho-physical organization, as in connection 
 with the development of skilled voluntary movements. As 
 Hobhouse suggests, we are not yet in a position to speak with 
 any confidence of the real character of the correspondence, if it 
 exists. 
 
 This survey of the facts offered in behalf of psycho-physical 
 recapitulation is far from complete, but the more prominent 
 illustrations have been referred to, and they probably warrant 
 tentative conclusions. On examination the more striking cases 
 are found to refer not to ancestral savage conditions, but to 
 
 « Mind in Evolution, p. 327, footnote. 
 
Human Infancy and the Recapitulation Theory 93 
 
 traits characteristic of the human species in general which have 
 been differently affected by the contingencies of historical 
 development. The civilized societies work differently with the 
 same human nature and by contrast the fundamental inborn 
 traits seem ancestral when they are only less trained. Other 
 cases rest upon analogies due to a confusion of inborn and ac- 
 quired elements in mental organization. Assertions of a phylo- 
 genetic rehearsal in the order of appearance of traits have been 
 made without empirical warrant. In the interests and activi- 
 ties which more especially characterize development as such, 
 the preparatory nature of immaturity is obvious, and this is 
 well illustrated in the group of cases which have had greatest 
 emphasis in connection with mental recapitulation. In the 
 matter of intelligence certain general considerations, as well as a 
 considerable amount of inductive study, give a fair presumption 
 of some degree of ontogenetic-phylogenetic correspondence in 
 this region. 
 
 4- Cultural Recapitulation. 
 
 Cultural recapitulation, or the theory of culture epochs, has 
 had a curious status in educational literature. While its sep- 
 arate origin has been acknowledged, and its integrity as a sub- 
 ject of discourse has been maintained by an independent title, 
 as a matter of practise the discussion of biological recapitula- 
 tion has encroached upon its territory with impunity and ap- 
 parently without full knowledge of what it was doing. For it 
 is clear that any application of biological recapitulation to men- 
 tal development as a whole deals directly with the question of 
 how its cultural acquisitions are assumed, whether in the order 
 followed by the race in the historical development of its cultural 
 products, or in some other way. And it is a commonplace 
 of the literature of recapitulation based upon the biological 
 analogy that the transition from barbarism to civilization con- 
 cludes the phylogenetic sequence. 
 
 Now the doctrine of biological recapitulation had reference 
 to ancestral species. By the statement that ontogeny re- 
 hearses phylogeny was meant that ontogeny repeats the suc- 
 cession of steps in the biological evolution of ancestors. This 
 was due to the force of heredity operating in descent despite 
 the modifications which marked the successive stages. But 
 the transition from primitive to civilized man, according to pre- 
 
94 The Recapitulation Theory and Human Infancy 
 
 vailing views, is not a biological progression. Primitive man 
 and civilized man represent the same species and the same men- 
 tality. The differences between the two are due in the main to 
 the unlike use of this common mentality by social and environ- 
 mental forces. Therefore historical development is not pbylo- 
 genetic, but ontogenetic, i. e., has taken place in individuals of 
 the same species. Biological recapitulation applied to the mind 
 of man must be held to refer to the alleged correspondence of 
 the hereditary sequence of psycho-physical functions in indi- 
 vidual development with the succession of homologous func- 
 tions in the series of ancestors. It applies then to the appear- 
 ance of reflexes and instincts, and to psycho-physical modes; 
 only indirectly to habits or acquired products represented in 
 culture. Our treatment of these matters has just been con- 
 cluded in the preceding section. We address ourselves at pre- 
 sent to the somewhat distinct issue of cultural recapitulation. 
 
 There is no need of recounting the history of the theory of 
 cultural recapitulation here. This has been done elsewhere. 45 
 The general bearing of the present discussion upon the theory 
 may, however, be briefly indicated. Cultural recapitulation 
 rests upon three distinct propositions : 1. The historical develop- 
 ment of culture, either as a whole or in particular liDes, was 
 determined in some degree by the inherent nature of the human 
 mind which permitted this order and no other. 2. There is an 
 inherent and necessary order in the acquisition of culture by 
 the immature mind. 3. The underlying necessity in develop- 
 ment is identical in the two series. 
 
 Let us consider the status of each proposition. 1. The con- 
 ception of an inevitable order in the development of culture 
 was apparently a derivative and special application of the idea 
 of biological evolution to social phenomena when the prestige 
 of the new doctrine was very great and when the sciences of 
 anthropology and sociology were yet in their early stages. The 
 application is due chiefly to Spencer, Tylor, and L. H. Morgan. 46 
 The empirical basis of the conception consisted of similarities 
 which were at first found conspicuous among all races, and more 
 especially of parallel lines of development in culture which were 
 
 a Vincent, Social Mind and Education, 1897, Chap. Ill and IV; Dewey, art. Culture 
 Epochs Theory, in Monroe's Cyclopedia of Education. See also, Henderson, Princi- 
 .ciples of Education, 1910, Chap. VI. 
 
 « Boas, Mind of Primitive Man, Chap. VII. 
 
Human Infancy and the Recapitulation Theory 95 
 
 considered general. Later investigation and discussion seems 
 to have sadly shaken the foundations of the conception. It has 
 been pointed out that similarities may be due to factors other 
 than common mentality, such as similar geographical environ- 
 ments, common points of radiation of culture, common tradi- 
 tions, and convergence from unlike sources of origin. Investi- 
 gation has dealt even more seriously with parallels in develop- 
 ment. The words of two anthropologists writing with high 
 authority will suggest the present situation in the science with 
 respect to the conceptions in question. 
 
 "The theory of parallel development, if it is to have any sig- 
 nificance, would require that among all branches of mankind 
 the steps of invention should be followed, at least approximately, 
 in the same order, and that no important gaps should be found. 
 The facts, so far as known at the present time, are entirely 
 contrary to this view. We are thus led to the conclusion that 
 the assumption of a uniform development of culture among all 
 the different races of man and among all tribal units is true in a 
 limited sense only." 47 
 
 The different races cannot be arranged, therefore, on a scale of 
 culture. 
 
 "While parallelisms of a certain kind were shown [by the 
 older students] to occur, this does not hold for parallelisms of 
 any degree of complexity and duration, nor for integral historic 
 processes, the individuality of which seems so conspicuous that 
 doubt prevails in the highest quarters as to whether anything 
 like historic laws in the strict sense will ever become more than 
 a desideratum." 
 
 "Whether the parallelisms refer to entire historical complexes 
 and embrace millenniums, or modestly comprise parallel develop- 
 ments of less extent and duration, when demonstrated they do 
 not constitute a solution, but a problem which has not so far 
 been successfully attacked." 48 
 
 It will be noticed that these writers do not wholly repudiate 
 parallelisms in development due presumably to common men- 
 tality. Their expressions have the force of setting positive 
 limits to the idea of their general prevalence held by the older 
 anthropologists. They also may not do justice to the fact that 
 there exists in their science an element or school laying great 
 stress upon the factor of common mind. Wundt's "Volker- 
 
 " Boas, op. tit., pp. 182, 195. 
 
 " Goldenweiser, Jour, of Amer. Folklore, July-Sept., 1913, pp. 281, 283. See also. 
 Boas, to Thomas, Source Book of Social Origins, 313-15. 
 
96 The Recapitulation Theory and Human Infancy 
 
 psychologie" represents the farthest advance in this direction, 
 and while this work is regarded as having the imperfections of a 
 pioneer effort, promise in this type of anthropological study is 
 not denied. As a matter of fact the sciences of anthropology 
 and psychology have not as yet been vitally joined in the in- 
 vestigation of culture, a significant thing in itself for our topic. 
 For the present it must be admitted that the idea of a neces- 
 sary order in historical development of an inclusive sort is some- 
 what under suspicion. The possibility, or rather the actual 
 existence of isolated cases of cultural parallels, seems to be 
 generally acknowledged. 49 
 
 2. Passing to the second proposition contained in the theory 
 of cultural recapitulation we find an equally uncertain situation. 
 That there is a determined order in some part of the progressive 
 development of the child mind no one doubts, and serious ef- 
 forts have been made with a view to its description. But it 
 cannot justly be held that a description of this order in general 
 terms has as yet been agreed upon by the students of child psy- 
 chology. More especially, the distinction necessary to an ap- 
 plication of the culture-epochs theory, between deferred inborn 
 or original traits and those traits which are to be regarded as 
 the results of exercise and cultural stimulation, has not yet 
 been determined with clearness, and until this distinction is 
 made it is obviously impossible to institute comparisons between 
 racial modes of cultural acquirement and genetic sequences 
 characteristic of the learning of children. Speaking broadly, 
 the many existing characterizations of "periods of development," 
 of "interests," or of "nascencies," etc., besides being too various 
 for general acceptance, deal indifferently with the appearance 
 of original traits and the development of acquisitions. Valu- 
 able special studies in certain lines are not wanting, notably 
 in language and drawing. Recently, in connection with mental 
 testing, progress towards maturity has been measured, but as yet 
 a qualitative description of this progress has not been under- 
 taken. On the whole, there is no question of genetic sequences 
 in many aspects of mental and cultural growth. We are, how- 
 ever, still in the dark as to just how these sequences should 
 be systematically described. 
 
 •• A philosophical and critical survey of the history of human progress conceived 
 largely in genetic terms is that of Santayana's Life of Reason (5 Vols., 1906). 
 
Human Infancy and the Recapitulation Theory 97 
 
 3. Notwithstanding the insecurity of the two primary as- 
 sumptions underlying the theory of culture-epochs, the develop- 
 ment of the individual and that of the race have been found by 
 serious students to have much in common. 50 A competent 
 examination of any one of the many applications of the theory of 
 cultural recapitulation is beyond the scope of this paper. They 
 range from religion to mathematics, and call in each case for 
 very special knowledge of the history of the branches of culture 
 in question, as well as for a broad equipment in the psychology 
 of the mental processes implicated. We can deal here with 
 but a few logical considerations. 
 
 It would not be surprising if the theory held that mature men 
 in a given society were required by their inherent nature to 
 follow in some degree the development of the culture that had 
 been evolved by mature minds in the course of history, for this 
 would imply, apart from the differentiating effects of environ- 
 mental influences, only some common mentality among adults 
 in the same species and some common elements in their modes 
 of progression in any given cultural direction. We have already 
 noticed the difference of opinion between the anthropologists 
 and psychologists with reference to this possibility. 
 
 But the theory goes beyond this. It asserts that unlike 
 ontogenetic periods may be compared with respect to their 
 cultural acquisitions. The child's mind is said to rehearse the 
 history of culture, which is essentially the expression of matur- 
 ity. Supposing, then, that a true genetic sequence had been 
 determined in the historical development of a given branch of 
 culture, based upon parallels among the different races of men, 
 is there a possible warrant for the assumption, made in the 
 culture-epochs theory, that a child's progress in this branch of 
 culture may be so accelerated that he can accomplish in his 
 immaturity what adults in the past could with difficulty attain 
 to? The answer to the question could be determined of course 
 only by an appeal to fact, but such acceleration is not impos- 
 sible if certain conditions be assumed. If the underlying or- 
 ganic basis for the historic progression has always been the 
 possession of childhood, and the conditions in civilized societies 
 
 >° See the account and references of Vincent, loc. cit. , also Ribot, Evolution of General 
 Ideas, 1899; Branford, A Study of Mathematical Education, 1908; Huey, Psychology 
 of Pedagogy of Reading, 1910, Part IX,; Baldwin, Thought and Things, Genetic 
 Logic, 1906. 
 
98 The Recapitulation Theory and Human Infancy 
 
 are now especially favorable to its functioning, it need not be 
 surprising if children should exhibit achievements that were 
 characteristic of adult societies in past times. For adults in 
 these societies were, on the present assumption, in a state of 
 arrest. From childhood they had had the capacity for advanc- 
 ing beyond the point of their actual adult attainments, but their 
 advance was prevented by the limitations of their cultural 
 environment. To illustrate, if in a genetic sequence symbolized 
 by the series a, b, c, d, e, f, childhood or youth has the inherent 
 capacity for rising to stage d, and does so in the highly favor- 
 able environment of civilized societies, it is easily conceivable 
 that adults in historical times, laboriously evolving their culture 
 independently, should remain life-long at points b or c. This 
 is no more than the equivalent of the thought that primitive 
 and historical men were relatively childlike, a familiar and wide- 
 spread idea among students of early cultural expressions. From 
 this it would follow that cultural recapitulation need not be 
 expected in any regions where organic differences between 
 children and adults exist. If certain branches of culture are 
 expressive of characteristically adolescent or mature attitudes 
 it will be idle to search for illustrations of their genetic rehearsal 
 in earlier periods. And since cultural recapitulation has to do 
 with acquisitions and processes of acquiring we must limit our 
 search for such recapitulations to the course of development 
 taken after the basic instinctive structures have begun their 
 functioning, at whatever period of growth this may be. 
 
 It is perhaps not possible as yet to characterize the disting- 
 uishable lines of growth within the complex field of cultural 
 acquisition. They are broadly represented by taste, moral 
 and social character, motor skill, and ideas, but these obviously 
 overlap. An adequate analysis of the general principles of 
 mental development will doubtless deal with much finer cate- 
 gories. It is worthy of notice that those who have done most 
 with the cultural recapitulation hypothesis have worked more 
 particularly in the field of thought and it is not impossible that 
 reasons may be found for regarding the plasticity represented by 
 thought and ideas as being available so early in life as to make 
 possible a genuine comparison of childish and historical pro- 
 cesses. And since ideas are most intimately related with every 
 aspect of cultural acquisition the possibility may be extended in 
 some degree to motor, moral, and aesthetic development. 
 
CHAPTER IV 
 
 CONCLUSION 
 
 The history of recapitulation is an instructive one. A prin- 
 ciple of limited application within the field of its origin was 
 elevated to a position of wide generality, and so gave rise to a 
 conception in the main misleading. Carried into a new terri- 
 tory without a sufficient examination of its merits, it was ap- 
 plied broadly as an explanatory principle and thus distributed 
 its misleading influence beyond its own borders. 
 
 Disregarding the qualifications which were forced upon it by 
 recalcitrant facts, the conception represented a view of individual 
 development as successively extended in the course of evolu- 
 tion, in such fashion that in any ontogeny the earliest features 
 are oldest, the later ones in succession increasingly recent. Thus 
 embryogeny as a period was oldest, infancy less old, and matur- 
 ity the last to evolve. From this form the conception degener- 
 ated to a less and less chroDological notion, until it came to mean 
 often no more than that any particular feature in development 
 which had an historical rather than a present reference was 
 illustrative of it. 
 
 A more thorough consideration of the facts has led to a view 
 of development essentially contradictory of this recapitulatory 
 one. Ontogeny represents the ancient life-cycle which as such 
 has been transmitted from the beginning. The chronological 
 sequence from egg to maturity is not a rehearsal of a like his- 
 torical series of events throughout the phylogeny of species; it 
 is but the recurrence of an order which has been repeated in the 
 lifetime of each individual from the beginning. In general, the 
 effect of the modifications induced by germinal mutations and 
 selection in the successive ontogenies constituting the phylo- 
 geny, was to alter these ontogenies, to make them over, and to 
 destroy the resemblance of later ones to their predecessors. 
 
 Still this alteration was not complete; neither was it regular 
 in its effects. Some very ancient forms are still hinted at in 
 
 99 
 
100 The Recapitulation Theory and Human Infancy 
 
 existing ontogenies; more especially particular structures were 
 often retained through long periods of time with considerable 
 faithfulness. Because of the slowness with which modifications 
 occurred, any ontogeny repeats most of the features of its proxi- 
 mate ancestral ontogeny, and in general the record grows less 
 and less true of phyletic ontogenies with remoteness in descent. 
 Because any ontogeny thus throws some light upon earlier ones, 
 and particularly upon proximate ones, the facts of ontogeny 
 gathered together help to reconstruct the whole line of descent. 
 Probably this is what is often meant by the statement that on- 
 togeny is a record of phylogeny. The statement should read 
 that genetically related ontogenies when compared supply some 
 ground for reconstructing phylogenies. 
 
 Although the effect of mutation and selection was in general 
 productive of alteration of the life-cycle, evidence points to a 
 considerable amount of extension of the life-cycle coincidentally 
 with alteration. This happened at times with the form of the 
 organism as a whole, but more often with particular orgaDS or 
 structures. 
 
 These considerations apply to the period of infancy with 
 qualification. Infancy was evolved from an ancient life-cycle 
 which did not possess such a period, presumably during and 
 since the Age of Mammals. We can only guess as to the nature 
 of its origin. It may represent a modified later part of the 
 ancient embryogeny set over into the post-natal period, or it 
 may be a remodelled part of the ancient period of precocious 
 maturity, or it may be both. In any case it is probably not due 
 to the successive extension of the mature end of old ontogenies, 
 and there is no need presupposing evidence within it of such 
 extensions. 
 
 It is, rather, probably the ancient structure of maturity, 
 either in process of growth or in completion, shorn of and supple- 
 mented by those things which plasticity presupposes. In its 
 most ancient features, such as the emotional phases and involun- 
 tary rudiments of instinct, it probably retains the characteristics 
 of maturity. We have seen no reason for assigning differences 
 between human infancy and adulthood in these respects. As 
 for the rest, we may tentatively bring over the classification of 
 features employed by Duckworth in connection with human 
 embryogeny, as follows: 
 
Conclusion 101 
 
 The infantile condition as such explains many adjustments that 
 natural selection might have insisted upon — the early dependence, 
 both physical and mental, upon the mother; the later larger 
 degree of self-care and self-protection, through fearfulness, shy- 
 ness, greediness, and selfishness. Then there is the necessity of 
 preparing for the adult condition — the spontaneous interest in 
 self-practice, the close correlation of mental need and maturing 
 structure as exhibited in the succession of interests, followed by 
 the palpably preparatory conditions of puberty and adolescence. 
 Finally there remains the small group of vestiges and "recapit- 
 ulatory" cases referring to ancestral infantile necessities or 
 adult preparation no longer required. 
 
 The period of infancy can have then no single explanation. 
 Many factors have conspired to give it its peculiar character. 
 As time passes we may be able to speak of these with greater 
 assurance. For the moment we may conclude with reason- 
 able certainty that infancy is not as such older than maturity; 
 from the same starting point the two evolved together, the one 
 giving character to the other by reason of those improvements 
 which have entered upon the horizon of later evolution — those, 
 namely, of intelligence and sociability. Infancy is obviously 
 incomplete; it is older, apparently, only in the degree, yet to be 
 determined, in which the growth of intelligence is required to 
 follow a phylogenetic order. 
 
BOOKS AND ARTICLES CITED 
 
 Agassiz, L. Essay on Classification. Boston, 1857. 
 
 . Lowell Lectures. Boston, 1848. 
 
 Armstrong, A. C. Herder and Fiske on the Prolongation of Infancy. Phil. 
 Rev., Vol. 15, 1906, 59-64. 
 
 Baldwin, J. M. Mental Development in the Child and the Race. New 
 York, 1895. 
 
 . Development and Evolution. New York, 1902. 
 
 . Social and Ethical Interpretations. New York, 1907. 
 
 . Thought and Things, Vol. 1. New York, 1908. 
 
 Balfour, F. M. Treatise on Comparative Embryology. 2nd ed., London, 
 1885. 
 
 Bateson, W. Problems of Genetics. New Haven, 1913. 
 j __Batheb. The Theory of Recapitulation. Natural Science, Vol. 2, 1893. 
 
 Bernard, H. M. Some Neglected Factors in Evolution. New York and 
 London, 1911. 
 
 Boas, F. The Mind of Primitive Man. New York, 1911. 
 
 Bolsche, W. Haeckel, His Life and Works. Trans, by J. McCabe. Phila- 
 delphia, 1906. 
 
 Branford, B. A Study in Mathematical Education. Oxford, 1908. 
 
 Bucxman, S. S. Babies and Monkeys. Nineteenth Century, Vol. 36, 1894, 
 727-743. 
 
 Chamberltn, A. F. The Child: A Study in the Evolution of Man. London, 
 1900. 
 
 Cope, E. D. The Origin of the Fittest. New York, 1887. 
 
 . The Primary Factors of Organic Evolution. Chicago and London, 
 
 1896. 
 -^Ctjmings, E. R. Palaeontology and the Recapitulation Theory. Proceed- 
 ings, Indiana Academy of Science, 1908-09, 305-340. 
 
 Cunningham, J. T. Recapitulation. Science Progress, Vol. VI, 1897. 
 
 Darwin, C. The Origin of Specie* jfit-e d . , Lon don , -1859 ;-6th— ed., Lon- 
 don, 1872. 
 
 Dendt, A. Outlines of Evolutionary Biology. New York, 1912. 
 
 Deperet, C. The Transformations of the Animal World. Trans. New 
 York, 1909. 
 
 Dewey, J. Studies in Logical Theory. Chicago, 1903. 
 
 . Article, Culture Epochs Theory, Monroe's Cyclopedia of Edu- 
 cation, 1911. 
 
 Dbiesch, H. The Science and Philosophy of the Organism. Gifford Lec- 
 tures. London, 1908. 
 *>■ — Drummond, H. Ascent of Man. New York, 1894. 
 
 102 
 
Books and Articles Cited 103 
 
 ,^-BtTCKwoBTH, W. H. L. Morphology and Anthropology. Cambridge, 1904. 
 
 — . Studies in Anthropology. Cambridge, 1904. 
 
 Ewaht, J. C. The Development of the Skeleton and Limbs of the Horse. 
 Journ. Comp. Path, and Thewr., Vol. VII, 1894; the same, Journ. 
 Anal, and Physio., Vol. XXVIII, 189^4. 
 Fiske, J. Outlines of Cosmic Philosophy. 2 vols. Boston, 1875. 
 
 . Excursions of an Evolutionist. Boston, 1893. 
 
 . Century of Science. Boston, 1899. 
 
 Goldenweiseb, A. A. The Principle of Limited Possibilities in the Develop- 
 ment of Culture. Journ. of Amer. Folklore, Vol. 26, July-Sept., 
 
 1913, 2o9-290. 
 iggs. Kelps and the Recapitulation Theory. American Naturalist, Vol. 
 
 43, 1909. 
 Groos, K. The Play of Animals. Trans. New York, 1898. 
 
 . The Play of Man. Trans. New York, 1900. 
 
 Haeckel, E. Generelle Morphologie der Organismen. 2 vols. Berlin, 1866. 
 
 — . Evolution of Man. 2 vols., 5th ed. Trans. New York, 1910. 
 
 Hall, G. S. Adolescence. 2 vols. New York, 1904. 
 
 Henderson, E. N. Text-Book in the Principles of Education. New York, 
 
 1910. 
 Henderson, L. J. Fitness of the Environment. New York, 1913. 
 Hobhouse, L. T. Mind in Evolution. New York, 1901. 
 Holmes, S. J. The Evolution of Animal Intelligence. New York, 1911. 
 Huey, E. B. The Psychology and Pedagogy of Reading. New York, 1910. 
 Hckvt, C. H. The Recapitulation Theory. Natural Science, Vol. 2, 1893. 
 Huxley, T. H. Scientific Memoirs. New York, 1902-1908. 
 
 . Evolution and Ethics. New York, 1894. 
 
 Hyatt, A. Genesis of the Arietidae. Smithsonian Contributions to Knowl- 
 edge. Washington, 1890. 
 . The Phylogeny of an Acquired Characteristic. Proceedings, 
 
 Amer. Phil. Soc, 1893. 
 Jenkinson, J. W. Experimental Embryology. Oxford, 1909. 
 Kellicott, W. E. Text-Book of General Embryology. New York, 1913. 
 Kin<";, I. Psychology of Child Development. Chicago, 1904. 
 Kropotkin, P. Mutual Aid as a Factor in Evolution. London, 1903. 
 Lankester, E. R. The Significance of the Increased Size of the Cerebrum 
 
 in Recent as Compared v.ith Extinct Mammalia. Nature, Vol. 
 
 LXI, 1900, 624, 625. 
 
 . The Kingdom of Man. New York, 1907. 
 
 Macbbide, E. W. Sedgwick's Theory of the Embryonic Phase of Ontogeny 
 
 as an Aid to Phylogenetic Theory. Quart. Journ. Micros. Science, 
 
 Vol. 37, 1894-95, 325-342. 
 McDougall, W. Introduction to Social Psychology. London, 1908. 
 Marsh, O. C. Small Size of the Brain in Tertiary Mammals. Amer. Journ. 
 
 of Science, Vol. VIII, 1874; abstract in Nature, Vol. 32, p. 562. 
 Marshall, A. M. Biological Lectures and Addresses. London and New 
 
 York, 1894. 
 . Lectures on the Darwinian Theory. New York, 1894. 
 
104 Book Title 
 
 Mehz, J. T. History of European Thought in the Nineteenth Century. 
 
 3 vols. London, 1903-13. 
 Miall, L. C. Address to the Zoological Section of the British Association 
 
 for the Advancement of Science. Proceedings, 1897. 
 Minot, C. S. Laboratory Text-Book in Embryology. 2nd ed. Phila- 
 delphia, 1910. 
 Mitchell, P. C. The Childhood of Animals. New York, 1912. 
 Montgomery, T. H. Jr. The Analysis of Racial Descent in Animals. New 
 
 York, 1906. 
 Morgan, C. L. Habit and Instinct. New York, 1896. 
 
 . Animal Behavior. 2nd ed. New York, 1908. 
 
 Morgan, T. H. Regeneration. New York, 1901. 
 
 . Evolution and Adaptation. New York, 1903. 
 
 . Experimental Zoology. New York, 1910. 
 
 Muller, F. Facts and Arguments for Darwin. Trans. London, 1864. 
 Mumford, A. A. Survival Movements in Human Infancy. Brain, Vol. 
 
 20, 1897, 290-307. 
 Osborn, H. F. The Causes of Extinction of Mammalia. American Natur- 
 alist, Vol. XL, 1906, 769-795, 829-859. 
 Osborn, H. F. The Evolution of Mammalian Molar Teeth. New York, 
 
 1907. 
 . Phylogeny and Ontogeny of the Horns of Mammals. Science, 
 
 Vol. 35, 595-596. 
 Peter, K. Ueber die biologische Bedeutung embryonaler und rudimentarer 
 
 Organe. Archil) fur Entwicklungsmechanik, Vol. 30, 1910, 418- 
 
 442. 
 Pom/roN, E. B. Essays on Evolution, 1889-1907. Oxford, 1908. 
 Puffer, J. A. The Boy and His Gang. New York, 1912. 
 Ptchaft, W. P. The Infancy of Animals. New York, 1913. 
 Robinson, L. Infantile Atavism. Brit. Med. Journ., Dec., 5, 1891, 1226, 
 
 1227. 
 . Darwinism in the Nursery. Nineteenth Century, VoL 30, 1891, 
 
 831-842. 
 
 . The Meaning of a Baby's Footprint. Nineteenth Century, Vol. 
 
 31, 1892, 795-806. 
 . The Primitive Child. North Amer. Rev., Vol. CLIX, 1894, 467- 
 
 478. 
 Romanes, G. J. Mental Evolution in Animals. New York, 1885. 
 
 . Mental Evolution in Man. New York, 1889. 
 
 Rotce, J. Outlines of Psychology. New York, 1903. 
 Santayana, G. The Life of Reason. 5 vols. New York, 1906. 
 Sedgwick, A. On the Law of Development Commonly Known as von 
 
 Baer's Law. Quart. Journ. Micros. Science, Vol. 36, 1894, 
 
 35-52. 
 . The Influence of Darwin on the Study of Animal Embryology, 
 
 in Darwin and Modern Science (Seward editor). Cambridge, 
 
 1909. 
 —— — . Article, Embryology. Encyclopaedia Britannica, 11th edition. 
 
Books and Articles Cited 105 
 
 Shikx, M. W. Notes on the Development of a Child. 2 vols. Berkeley, 
 
 Cal., 1893-1907. 
 Smith, G. Primitive Animals. New York, 1912. 
 Smith, J. P. The Biogenetic Law from the Standpoint of Palaeontology. 
 
 Journ. of Geology, Vol. 8, 1900. 
 Spenceb, H. Principles of Biology. 2 vols. 1st ed., New York, 1866-7; 
 
 revised, New York, 1898-1900. 
 Somneb, W. G. Folkways. Boston, 1907. 
 Sutherland, A. Origin and Growth of the Moral Instinct. 2 vols. New 
 
 York, 1898. 
 Swift, E. J. Mind in the Making. New York, 1908. 
 Tarde, G. Lav.-s of Imitation. 2nd ed. Trans. New York, 1903. 
 Thomas, W. I. Source Book for Social Origins. Chicago, 1909. 
 Thobndike, E. L. The Original Nature of Man. New York, 1913. 
 Ttleb, J. M. Growth and Education. Boston, 1907. 
 Vincent, G. E. The Social Mind and Education. Chicago, 1897. 
 ion Buttel-Reepen, H. B. Man and His Forerunners. Trans. London 
 
 and New York, 1913. 
 von Zittel, K. Palaeontology and the Biogenetic Law. Natural Science, 
 
 Vol. 6, 1895, 305-312. 
 Wallace, A. R. Natural Selection and Tropical Nature. New York, 1891. 
 Washbubn, M. F. Animal Mind. New York, 1908. 
 Woodwabd, A. S. Outlines of Vertebrate Palaeontology. Cambridge, 1898.